diff --git a/src/_types.ts b/src/_types.ts
index 8d9591a..2b7e164 100644
--- a/src/_types.ts
+++ b/src/_types.ts
@@ -1679,6 +1679,8 @@ export interface WriteOptions {
   /** String storage mode. Default: "shared"
    *  - "shared": shared string table (smaller files with repeated strings)
    *  - "inline": inline strings per cell (faster write, larger files)
+   *
+   *  Rich text follows the same choice (#602).
    */
   stringMode?: "shared" | "inline"
   /** VBA project binary (vbaProject.bin) to embed. Output becomes macro-enabled (.xlsm). */
diff --git a/src/xlsx/worksheet-writer.ts b/src/xlsx/worksheet-writer.ts
index 381cc64..e70126f 100644
--- a/src/xlsx/worksheet-writer.ts
+++ b/src/xlsx/worksheet-writer.ts
@@ -153,8 +153,12 @@ export function rangeRef(
 export interface SharedStringsCollector {
   /** Get or add a string, return its index */
   add(value: string): number
-  /** Get all strings in order */
+  /** Get or add a rich string, return its index */
+  addRich(runs: RichTextRun[]): number
+  /** Get all strings in order. A rich string is its runs' text joined. */
   getAll(): string[]
+  /** The `<r>` runs of each rich string, by index */
+  getRich(): ReadonlyMap<number, string>
   /** Get count */
   count(): number
 }
@@ -162,6 +166,11 @@ export interface SharedStringsCollector {
 export function createSharedStrings(): SharedStringsCollector {
   const strings: string[] = []
   const indexMap = new Map<string, number>()
+  // Rich strings are keyed by their serialized runs, in a map of their
+  // own: "Bold normal" in bold and the plain "Bold normal" are different
+  // entries, while two cells with equal runs share one. See #602.
+  const richIndexMap = new Map<string, number>()
+  const richXml = new Map<number, string>()
 
   function add(value: string): number {
     const existing = indexMap.get(value)
@@ -173,15 +182,31 @@ export function createSharedStrings(): SharedStringsCollector {
     return idx
   }
 
+  function addRich(runs: RichTextRun[]): number {
+    const xml = serializeRichTextRuns(runs).join("")
+    const existing = richIndexMap.get(xml)
+    if (existing !== undefined) return existing
+
+    const idx = strings.length
+    strings.push(runs.map((run) => run.text).join(""))
+    richIndexMap.set(xml, idx)
+    richXml.set(idx, xml)
+    return idx
+  }
+
   function getAll(): string[] {
     return strings
   }
 
+  function getRich(): ReadonlyMap<number, string> {
+    return richXml
+  }
+
   function count(): number {
     return strings.length
   }
 
-  return { add, getAll, count }
+  return { add, addRich, getAll, getRich, count }
 }
 
 /** Generate xl/sharedStrings.xml */
@@ -193,9 +218,13 @@ export function writeSharedStringsXml(sharedStrings: SharedStringsCollector): st
     return xmlDocument("sst", { xmlns: NS_SPREADSHEET, count: 0, uniqueCount: 0 }, "")
   }
 
+  const rich = sharedStrings.getRich()
   const children: string[] = []
-  for (const str of strings) {
-    children.push(xmlElement("si", undefined, [xmlTextElement(str)]))
+  for (let i = 0; i < count; i++) {
+    // A rich `<si>` holds the same `<r>` runs as an inline `<is>`
+    // (§18.4.8, §18.3.1.53).
+    const runs = rich.get(i)
+    children.push(xmlElement("si", undefined, runs ?? [xmlTextElement(strings[i])]))
   }
 
   return xmlDocument("sst", { xmlns: NS_SPREADSHEET, count, uniqueCount: count }, children)
@@ -961,8 +990,13 @@ export function serializeCell(
 
   const ref = cellRef(row, col)
 
-  // Rich text cell (inline string)
+  // Rich text cell. It follows `stringMode` like plain text: it used to be
+  // inline whatever the mode, so tools that only read the shared string
+  // table never saw it, and Excel itself puts rich text there. See #602.
   if (richText && richText.length > 0) {
+    if (!inlineStrings) {
+      return simpleCell(ref, styleIdx, "s", String(sharedStrings.addRich(richText)))
+    }
     const cellAttrs: Record<string, string | number> = { r: ref, t: "inlineStr" }
     if (styleIdx !== 0) cellAttrs["s"] = styleIdx
     const isContent = serializeRichTextRuns(richText)
@@ -1527,7 +1561,7 @@ function serializeColorAttrs(color: Color): Record<string, string | number> {
 
 // ── Rich Text Serialization ──────────────────────────────────────────
 
-/** Serialize an array of RichTextRun into XML elements for an <is> (inline string) block */
+/** Serialize an array of RichTextRun into the `<r>` elements of an `<is>` or a shared `<si>` */
 function serializeRichTextRuns(runs: RichTextRun[]): string[] {
   const elements: string[] = []
 
diff --git a/test/batch-fixes.test.ts b/test/batch-fixes.test.ts
index 9750657..abab47f 100644
--- a/test/batch-fixes.test.ts
+++ b/test/batch-fixes.test.ts
@@ -127,7 +127,15 @@ describe("#89: Rich text writing", () => {
       ]),
     }
 
-    const xml = writeXml(sheet)
+    // The inline form; rich text in the shared string table is #602.
+    const xml = writeWorksheetXml(
+      sheet,
+      createStylesCollector(),
+      createSharedStrings(),
+      undefined,
+      undefined,
+      true,
+    ).xml
     const doc = parseXml(xml)
 
     const sheetData = findChild(doc, "sheetData")
diff --git a/test/coverage-xlsx-writer.test.ts b/test/coverage-xlsx-writer.test.ts
index a2c2cff..1720b52 100644
--- a/test/coverage-xlsx-writer.test.ts
+++ b/test/coverage-xlsx-writer.test.ts
@@ -114,7 +114,7 @@ describe("styled cells of every value shape", () => {
   const styled: CellStyle = { font: { bold: true } }
 
   it("keeps the style index on a rich-text cell", async () => {
-    const xml = await sheetXml({
+    const sheet: WriteSheet = {
       name: "S",
       cells: cellMap([
         [
@@ -125,9 +125,13 @@ describe("styled cells of every value shape", () => {
           },
         ],
       ]),
-    })
+    }
 
-    expect(xml).toMatch(/<c r="A1" t="inlineStr" s="\d+">/)
+    // Shared by default, inline on request — see #602.
+    expect(await sheetXml(sheet)).toMatch(/<c r="A1" t="s" s="\d+"><v>0<\/v><\/c>/)
+    expect(await sheetXml(sheet, { stringMode: "inline" })).toMatch(
+      /<c r="A1" t="inlineStr" s="\d+">/,
+    )
   })
 
   it("keeps the style index on an error cell", async () => {
@@ -329,29 +333,34 @@ describe("sheet-level OOXML blocks", () => {
 
 describe("rich text run properties", () => {
   it("writes vertAlign, family, charset and scheme into <rPr>", async () => {
-    const xml = await sheetXml({
-      name: "S",
-      cells: cellMap([
-        [
-          "0,0",
-          {
-            richText: [
-              { text: "E=mc" },
-              {
-                text: "2",
-                font: {
-                  vertAlign: "superscript",
-                  family: 2,
-                  charset: 204,
-                  scheme: "minor",
-                  color: { indexed: 10 },
+    // Inline, so the runs are in the sheet; the shared form is the same
+    // `serializeRichTextRuns` output inside an `<si>` (#602).
+    const xml = await sheetXml(
+      {
+        name: "S",
+        cells: cellMap([
+          [
+            "0,0",
+            {
+              richText: [
+                { text: "E=mc" },
+                {
+                  text: "2",
+                  font: {
+                    vertAlign: "superscript",
+                    family: 2,
+                    charset: 204,
+                    scheme: "minor",
+                    color: { indexed: 10 },
+                  },
                 },
-              },
-            ],
-          },
-        ],
-      ]),
-    })
+              ],
+            },
+          ],
+        ]),
+      },
+      { stringMode: "inline" },
+    )
 
     expect(xml).toContain('<vertAlign val="superscript"/>')
     expect(xml).toContain('<family val="2"/>')
diff --git a/test/one-cell-serializer.test.ts b/test/one-cell-serializer.test.ts
index 569bb62..3d6f2c1 100644
--- a/test/one-cell-serializer.test.ts
+++ b/test/one-cell-serializer.test.ts
@@ -146,8 +146,11 @@ describe("the authoring path did not regress", () => {
     })
 
     const xml = await sheetXml(bytes)
+    const sst = new TextDecoder().decode(await new ZipReader(bytes).extract("xl/sharedStrings.xml"))
 
-    expect(xml).toContain("<is>")
+    // Shared string mode, so the runs are in the table (#602).
+    expect(xml).toContain('<c r="A1" t="s"><v>0</v></c>')
+    expect(sst).toContain("<si><r><rPr><b/></rPr><t>bold</t></r></si>")
     expect(xml).toContain('t="shared"')
     expect(xml).toContain('si="0"')
     expect(xml).toMatch(/cm="\d+"/)
diff --git a/test/rich-text-shared-strings.test.ts b/test/rich-text-shared-strings.test.ts
new file mode 100644
index 0000000..d3ae999
--- /dev/null
+++ b/test/rich-text-shared-strings.test.ts
@@ -0,0 +1,121 @@
+import { describe, expect, it } from "vitest"
+import { writeXlsx } from "../src/xlsx/writer"
+import { readXlsx } from "../src/xlsx/reader"
+import { openXlsx, saveXlsx } from "../src/xlsx/roundtrip"
+import { ZipReader } from "../src/zip/reader"
+import type { Cell, RichTextRun, WriteOptions, WriteSheet } from "../src/_types"
+
+// ═══════════════════════════════════════════════════════════════════════
+// Rich text ignored `stringMode`. Plain text went to xl/sharedStrings.xml
+// in the default "shared" mode, but a rich text cell was always written
+// inline:
+//
+//   <c r="A2" t="inlineStr"><is><r><rPr><b/></rPr><t>Bold</t></r>…</is></c>
+//
+// That is valid, but anything that only reads the shared string table —
+// template engines, find/replace, string indexing — never saw the rich
+// cells, and it is not what Excel writes. In shared mode a rich string is
+// now an `<si>` holding the same `<r>` runs (ECMA-376 Part 1 §18.4.8) and
+// the cell is `t="s"`. Inline mode is unchanged. See #602.
+// ═══════════════════════════════════════════════════════════════════════
+
+const decoder = new TextDecoder("utf-8")
+
+async function part(buf: Uint8Array, path: string): Promise<string> {
+  return decoder.decode(await new ZipReader(buf).extract(path))
+}
+
+const BOLD_RUNS: RichTextRun[] = [{ text: "Bold", font: { bold: true } }, { text: " normal" }]
+const BOLD_RUNS_XML = '<r><rPr><b/></rPr><t>Bold</t></r><r><t xml:space="preserve"> normal</t></r>'
+
+function write(
+  cells: Array<[string, Partial<Cell>]>,
+  rows: WriteSheet["rows"] = [],
+  options: Omit<WriteOptions, "sheets"> = {},
+): Promise<Uint8Array> {
+  return writeXlsx({ sheets: [{ name: "S", rows, cells: new Map(cells) }], ...options })
+}
+
+describe("rich text in shared string mode (#602)", () => {
+  it('writes the runs into the shared string table and the cell as t="s"', async () => {
+    const buf = await write([["1,0", { richText: BOLD_RUNS }]], [["Plain"]])
+
+    const sheet = await part(buf, "xl/worksheets/sheet1.xml")
+    expect(sheet).toContain('<c r="A2" t="s"><v>1</v></c>')
+    expect(sheet).not.toContain("inlineStr")
+
+    const sst = await part(buf, "xl/sharedStrings.xml")
+    expect(sst).toContain('count="2" uniqueCount="2"')
+    expect(sst).toContain(`<si><t>Plain</t></si><si>${BOLD_RUNS_XML}</si>`)
+  })
+
+  it("keeps the style index on a shared rich text cell", async () => {
+    const buf = await write([["0,0", { richText: BOLD_RUNS, style: { font: { italic: true } } }]])
+
+    const sheet = await part(buf, "xl/worksheets/sheet1.xml")
+    expect(sheet).toMatch(/<c r="A1" t="s" s="[1-9]\d*"><v>0<\/v><\/c>/)
+  })
+
+  it("shares one entry between identical rich strings, apart from plain text", async () => {
+    const buf = await write([
+      ["0,0", { richText: BOLD_RUNS }],
+      ["0,1", { value: "Bold normal" }],
+      ["0,2", { richText: [{ text: "Bold", font: { bold: true } }, { text: " normal" }] }],
+      ["0,3", { richText: [{ text: "Bold", font: { italic: true } }, { text: " normal" }] }],
+    ])
+
+    const sheet = await part(buf, "xl/worksheets/sheet1.xml")
+    expect(sheet).toContain('<c r="A1" t="s"><v>0</v></c>')
+    // Same text, no runs: a different string as far as the table goes.
+    expect(sheet).toContain('<c r="B1" t="s"><v>1</v></c>')
+    // Equal runs, separate array: the same entry.
+    expect(sheet).toContain('<c r="C1" t="s"><v>0</v></c>')
+    // Same text, different formatting: a new entry.
+    expect(sheet).toContain('<c r="D1" t="s"><v>2</v></c>')
+
+    const sst = await part(buf, "xl/sharedStrings.xml")
+    expect(sst).toContain('count="3" uniqueCount="3"')
+  })
+
+  it("writes the shared string part when rich text is the only text", async () => {
+    const buf = await write([["0,0", { richText: BOLD_RUNS }]])
+    const zip = new ZipReader(buf)
+
+    expect(zip.has("xl/sharedStrings.xml")).toBe(true)
+    expect(await part(buf, "[Content_Types].xml")).toContain('PartName="/xl/sharedStrings.xml"')
+    expect(await part(buf, "xl/_rels/workbook.xml.rels")).toContain('Target="sharedStrings.xml"')
+    expect(await part(buf, "xl/sharedStrings.xml")).toContain(`<si>${BOLD_RUNS_XML}</si>`)
+  })
+
+  it("reads the rich text back from the shared string table", async () => {
+    const buf = await write([["0,0", { richText: BOLD_RUNS }]])
+
+    const cell = (await readXlsx(buf)).sheets[0].cells?.get("0,0")
+    expect(cell?.type).toBe("richText")
+    expect(cell?.value).toBe("Bold normal")
+    expect(cell?.richText).toEqual(BOLD_RUNS)
+  })
+
+  it("leaves inline mode as it was", async () => {
+    const buf = await write([["1,0", { richText: BOLD_RUNS }]], [["Plain"]], {
+      stringMode: "inline",
+    })
+
+    const sheet = await part(buf, "xl/worksheets/sheet1.xml")
+    expect(sheet).toContain(`<c r="A2" t="inlineStr"><is>${BOLD_RUNS_XML}</is></c>`)
+    expect(new ZipReader(buf).has("xl/sharedStrings.xml")).toBe(false)
+  })
+
+  it("saveXlsx writes rich text into the shared string table too", async () => {
+    // saveXlsx always writes shared strings, so a rich cell read from an
+    // inline-only file moves into the table.
+    const original = await write([["0,0", { richText: BOLD_RUNS }]], [], { stringMode: "inline" })
+    const saved = await saveXlsx(await openXlsx(original))
+
+    expect(await part(saved, "xl/worksheets/sheet1.xml")).toContain('<c r="A1" t="s"><v>0</v></c>')
+    expect(await part(saved, "xl/sharedStrings.xml")).toContain(`<si>${BOLD_RUNS_XML}</si>`)
+
+    const cell = (await readXlsx(saved)).sheets[0].cells?.get("0,0")
+    expect(cell?.richText).toEqual(BOLD_RUNS)
+  })
+})
diff --git a/test/rich-text-write.test.ts b/test/rich-text-write.test.ts
index f9bbf7d..f6f8782 100644
--- a/test/rich-text-write.test.ts
+++ b/test/rich-text-write.test.ts
@@ -20,10 +20,13 @@ function getElementText(el: { children: Array<unknown> }): string {
   return el.children.filter((c: unknown) => typeof c === "string").join("")
 }
 
+// Inline mode, so the runs can be read off the cell's `<is>`. The shared
+// form writes the same runs into an `<si>` — see
+// rich-text-shared-strings.test.ts (#602).
 function writeXml(sheet: WriteSheet): string {
   const styles = createStylesCollector()
   const ss = createSharedStrings()
-  const result = writeWorksheetXml(sheet, styles, ss)
+  const result = writeWorksheetXml(sheet, styles, ss, undefined, undefined, true)
   return result.xml
 }
 
@@ -308,7 +311,9 @@ describe("rich text write — mixed sheet", () => {
       cells,
     }
 
-    const xml = writeXml(sheet)
+    // Shared mode, the default: both strings go to the table (#602).
+    const ss = createSharedStrings()
+    const xml = writeWorksheetXml(sheet, createStylesCollector(), ss).xml
     const doc = parseSheet(xml)
     const sheetData = findChild(doc, "sheetData")
     const rows = findChildren(sheetData, "row")
@@ -317,9 +322,13 @@ describe("rich text write — mixed sheet", () => {
     const c1 = findChild(rows[0], "c")
     expect(c1.attrs["t"]).toBe("s")
 
-    // Row 2: rich text (inlineStr)
+    // Row 2: rich text, a separate shared string carrying its runs
     const c2 = findChild(rows[1], "c")
-    expect(c2.attrs["t"]).toBe("inlineStr")
+    expect(c2.attrs["t"]).toBe("s")
+    expect(getElementText(findChild(c2, "v"))).toBe("1")
+    expect(ss.getAll()).toEqual(["Plain string", "Bold text"])
+    expect(ss.getRich().get(0)).toBeUndefined()
+    expect(ss.getRich().get(1)).toContain("<r><rPr><b/></rPr><t>Bold</t></r>")
 
     // Row 3: number
     const c3 = findChild(rows[2], "c")
diff --git a/test/xml-space-preserve.test.ts b/test/xml-space-preserve.test.ts
index 2c2226e..77d7a74 100644
--- a/test/xml-space-preserve.test.ts
+++ b/test/xml-space-preserve.test.ts
@@ -64,11 +64,18 @@ describe("xml:space=preserve on every <t> that needs it", () => {
 
   it("declares it on a rich-text run", async () => {
     const cells = new Map([["0,0", { richText: [{ text: PADDED, font: { bold: true } }] }]])
-    const bytes = await writeXlsx({ sheets: [{ name: "S", rows: [[null]], cells }] })
-
-    const xml = await part(bytes, "xl/worksheets/sheet1.xml")
-
-    expect(xml).toContain(`<t xml:space="preserve">${PADDED}</t>`)
+    const sheets = [{ name: "S", rows: [[null]], cells }]
+
+    // Shared mode puts the runs in the string table (#602), inline mode
+    // in the cell.
+    const shared = await writeXlsx({ sheets })
+    expect(await part(shared, "xl/sharedStrings.xml")).toContain(
+      `<t xml:space="preserve">${PADDED}</t>`,
+    )
+    const inline = await writeXlsx({ stringMode: "inline", sheets })
+    expect(await part(inline, "xl/worksheets/sheet1.xml")).toContain(
+      `<t xml:space="preserve">${PADDED}</t>`,
+    )
   })
 
   it("declares it on a streamed inline string", async () => {