diff --git a/.changeset/split-meow-mixed-currency-guard.md b/.changeset/split-meow-mixed-currency-guard.md
new file mode 100644
index 000000000..3d60df7b6
--- /dev/null
+++ b/.changeset/split-meow-mixed-currency-guard.md
@@ -0,0 +1,5 @@
+---
+'@app/split-meow': patch
+---
+
+修正混幣行程（同一行程記到多種幣別）會把不同幣別金額直接相加、顯示錯誤總額與結算的問題；偵測到多幣別時改顯示警告並隱藏無效的總額與結算（含分享文字），引導使用者改用單一幣別記帳。
diff --git a/apps/split-meow/src/components/HistoryTab.tsx b/apps/split-meow/src/components/HistoryTab.tsx
index 438605538..426b2fac6 100644
--- a/apps/split-meow/src/components/HistoryTab.tsx
+++ b/apps/split-meow/src/components/HistoryTab.tsx
@@ -183,6 +183,8 @@ export function HistoryTab() {
   const tripCurrency: CurrencyCode = tripExpenses[tripExpenses.length - 1]?.currency ?? currency;
   // 取得單筆記錄的顯示幣別（優先使用記帳當下快照，舊資料 fallback 主導幣別）。
   const expenseCurrency = (exp: ExpenseRecord): CurrencyCode => exp.currency ?? tripCurrency;
+  // 混幣行程：跨幣別直接相加的總額與結算為無效運算，改顯示警告而非誤導數字。
+  const isMixedCurrency = new Set(tripExpenses.map((exp) => expenseCurrency(exp))).size > 1;
 
   // 計算各人餘額
   const balances: Record<string, number> = {};
@@ -222,7 +224,9 @@ export function HistoryTab() {
     const lines: string[] = [
       `🐾 喵喵分帳 — ${tripName}`,
       `${'─'.repeat(24)}`,
-      `💰 總花費：${formatAmount(totalSpent, tripCurrency)}`,
+      isMixedCurrency
+        ? `⚠️ ${t('history.mixed_currency_warning')}`
+        : `💰 總花費：${formatAmount(totalSpent, tripCurrency)}`,
       '',
     ];
     if (tripExpenses.length > 0) {
@@ -239,7 +243,7 @@ export function HistoryTab() {
       });
       lines.push('');
     }
-    if (settlements.length > 0) {
+    if (settlements.length > 0 && !isMixedCurrency) {
       lines.push(`💸 結清方式`);
       settlements.forEach((s) => {
         const from = members.find((m) => m.id === s.from)?.name ?? s.from;
@@ -281,9 +285,15 @@ export function HistoryTab() {
             <span className="text-xs font-medium uppercase tracking-widest text-primary mb-1 block">
               {t('history.total_spent')}
             </span>
-            <h2 className="text-4xl font-medium text-on-surface tracking-tight">
-              {formatAmount(totalSpent, tripCurrency)}
-            </h2>
+            {isMixedCurrency ? (
+              <p className="text-sm font-medium text-error leading-snug">
+                {t('history.mixed_currency_warning')}
+              </p>
+            ) : (
+              <h2 className="text-4xl font-medium text-on-surface tracking-tight">
+                {formatAmount(totalSpent, tripCurrency)}
+              </h2>
+            )}
           </div>
           <div className="mt-6 flex items-center justify-between gap-2">
             <div className="flex items-center gap-2">
@@ -327,7 +337,7 @@ export function HistoryTab() {
       </section>
 
       {/* 結清方式 */}
-      {settlements.length > 0 && (
+      {settlements.length > 0 && !isMixedCurrency && (
         <section className="mb-10">
           <h3 className="text-xs font-medium uppercase tracking-widest text-outline px-2 mb-4">
             {t('history.settlements')}
diff --git a/apps/split-meow/src/components/__tests__/HomeAndHistorySmoke.test.tsx b/apps/split-meow/src/components/__tests__/HomeAndHistorySmoke.test.tsx
index 647d6e714..7c5b47892 100644
--- a/apps/split-meow/src/components/__tests__/HomeAndHistorySmoke.test.tsx
+++ b/apps/split-meow/src/components/__tests__/HomeAndHistorySmoke.test.tsx
@@ -223,4 +223,46 @@ describe('HistoryTab', () => {
     // Should render settlement amounts somewhere
     expect(document.body).toBeTruthy();
   });
+
+  it('混幣行程顯示警告並隱藏總額與結算（避免跨幣別錯誤加總）', () => {
+    useStore.setState({
+      expenses: [
+        { ...EXPENSE_1, id: 'mix-twd', currency: 'TWD', totalAmount: 300 },
+        {
+          id: 'mix-krw',
+          tripId: 'trip-1',
+          type: 'split_evenly' as const,
+          participantIds: ['me', 'm1'],
+          paidBy: 'm1',
+          totalAmount: 9000,
+          perPersonAmounts: { me: 4500, m1: 4500 },
+          note: '',
+          createdAt: Date.now() + 1,
+          currency: 'KRW',
+        },
+      ],
+    });
+    renderWith(<HistoryTab />);
+    expect(screen.getByText(i18n.t('history.mixed_currency_warning'))).toBeInTheDocument();
+    // 結算區塊標題不應出現：跨幣別結算為無效運算，不得顯示誤導金額。
+    expect(screen.queryByText(i18n.t('history.settlements'))).not.toBeInTheDocument();
+  });
+
+  it('單一幣別行程不顯示混幣警告', () => {
+    useStore.setState({
+      expenses: [
+        { ...EXPENSE_1, id: 'same-1', currency: 'TWD' },
+        {
+          ...EXPENSE_1,
+          id: 'same-2',
+          currency: 'TWD',
+          paidBy: 'm1',
+          totalAmount: 60,
+          perPersonAmounts: { me: 30, m1: 30 },
+        },
+      ],
+    });
+    renderWith(<HistoryTab />);
+    expect(screen.queryByText(i18n.t('history.mixed_currency_warning'))).not.toBeInTheDocument();
+  });
 });
diff --git a/apps/split-meow/src/i18n.ts b/apps/split-meow/src/i18n.ts
index 3fdaf5bf8..8ee02b4a0 100644
--- a/apps/split-meow/src/i18n.ts
+++ b/apps/split-meow/src/i18n.ts
@@ -33,6 +33,7 @@ const resources = {
         total_spent: '總花費',
         members_count: '由 {{count}} 位探險家分攤',
         settlements: '結清方式',
+        mixed_currency_warning: '此行程含多種幣別，無法合併總額與結算，請改用單一幣別記帳',
         pay_to: '{{from}} 付給 {{to}}',
         balances: '各人結算',
         owed: '應收',
@@ -123,6 +124,8 @@ const resources = {
         total_spent: 'Total Spent',
         members_count: '{{count}} adventurers splitting',
         settlements: 'How to Settle',
+        mixed_currency_warning:
+          'This trip mixes currencies; totals and settlement cannot be combined. Use a single currency.',
         pay_to: '{{from}} pays {{to}}',
         balances: 'Balances',
         owed: 'Receives',
@@ -213,6 +216,8 @@ const resources = {
         total_spent: '총 지출',
         members_count: '{{count}}명이 분담',
         settlements: '정산 방법',
+        mixed_currency_warning:
+          '이 여행에는 여러 통화가 섞여 있어 합계와 정산을 합칠 수 없습니다. 단일 통화를 사용하세요.',
         pay_to: '{{from}} → {{to}}',
         balances: '개인 정산',
         owed: '받을 돈',
@@ -303,6 +308,8 @@ const resources = {
         total_spent: '総支出',
         members_count: '{{count}}人で割り勘',
         settlements: '精算方法',
+        mixed_currency_warning:
+          'この旅行は複数の通貨が混在しており、合計と精算を統合できません。単一通貨を使用してください。',
         pay_to: '{{from}} → {{to}}',
         balances: '各自の精算',
         owed: '受け取り',