diff --git a/app/Services/Transaction/TransactionService.php b/app/Services/Transaction/TransactionService.php
index f96e78f..4354430 100644
--- a/app/Services/Transaction/TransactionService.php
+++ b/app/Services/Transaction/TransactionService.php
@@ -305,6 +305,17 @@ class TransactionService
                 if ($slot) {
                     $slot->decrement('stock');
 
+                    // 售完（庫存歸 0）即清空效期與批號，避免舊批貨效期殘留。
+                    // 場景：日後管理員只補 stock 未改 expiry_date 時，update_inventory 才不會
+                    // 把過期日一起下發、把新批貨誤鎖成「暫不販售」。與機台端「賣完清效期」對稱。
+                    // 純加法：僅在仍有殘留值時才寫，不影響既有扣庫存行為。
+                    if ($slot->stock <= 0 && ($slot->expiry_date !== null || $slot->batch_no !== null)) {
+                        $slot->update([
+                            'expiry_date' => null,
+                            'batch_no' => null,
+                        ]);
+                    }
+
                     $type = \App\Models\Machine\MachineStockMovement::TYPE_SALE;
 
                     $this->machineService->recordStockMovement(
diff --git a/tests/Feature/Transaction/ExpiryClearOnSelloutMysqlTest.php b/tests/Feature/Transaction/ExpiryClearOnSelloutMysqlTest.php
new file mode 100644
index 0000000..1bfe5dd
--- /dev/null
+++ b/tests/Feature/Transaction/ExpiryClearOnSelloutMysqlTest.php
@@ -0,0 +1,101 @@
+<?php
+
+namespace Tests\Feature\Transaction;
+
+use App\Models\Machine\Machine;
+use App\Models\System\Company;
+use App\Services\Transaction\TransactionService;
+use Illuminate\Foundation\Testing\RefreshDatabase;
+use Illuminate\Support\Facades\DB;
+use Tests\TestCase;
+
+/**
+ * 售完（庫存歸 0）自動清空效期/批號 —— 需 MySQL（recordDispense 內部寫
+ * machine_stock_movements，其 type enum 為 MySQL-only DDL，sqlite :memory: 無法驗）。執行:
+ *
+ *   ./vendor/bin/sail test -c phpunit.mysql.xml --filter ExpiryClearOnSelloutMysqlTest
+ *
+ * 在預設 sqlite 套件中自動 skip,不影響主套件綠燈。
+ *
+ * 動機：機台端「賣完清效期」已做，但 B009 補貨上報不回傳 expiry，後台若殘留舊效期，
+ * 日後管理員只補 stock 未改效期 → update_inventory 把過期日下發 → 新批貨被誤鎖。
+ * 故後台扣庫存歸 0 時亦須清效期，與機台端對稱。
+ */
+class ExpiryClearOnSelloutMysqlTest extends TestCase
+{
+    use RefreshDatabase;
+
+    private Company $company;
+    private TransactionService $service;
+
+    protected function setUp(): void
+    {
+        parent::setUp();
+
+        if (DB::connection()->getDriverName() !== 'mysql') {
+            $this->markTestSkipped('需 MySQL:machine_stock_movements.type enum 為 MySQL-only DDL。');
+        }
+
+        $this->company = Company::create(['name' => 'Test Company']);
+        $this->service = app(TransactionService::class);
+    }
+
+    private function dispense(string $serial, string $slotNo): array
+    {
+        return [
+            'serial_no' => $serial,
+            'slot_no' => $slotNo,
+            'product_id' => 101,
+            'amount' => 50,
+            'dispense_status' => 1,
+        ];
+    }
+
+    /** 庫存賣到 0 → 效期與批號被清空。 */
+    public function test_clears_expiry_and_batch_when_stock_hits_zero(): void
+    {
+        $serial = '1234567890';
+        $machine = Machine::factory()->create([
+            'company_id' => $this->company->id,
+            'serial_no' => $serial,
+        ]);
+        $slot = $machine->slots()->create([
+            'slot_no' => '1',
+            'stock' => 1,
+            'max_stock' => 10,
+            'expiry_date' => '2030-12-31',
+            'batch_no' => 'B-001',
+        ]);
+
+        $this->service->recordDispense($this->dispense($serial, '1'));
+
+        $fresh = $slot->fresh();
+        $this->assertEquals(0, $fresh->stock, '庫存應扣為 0');
+        $this->assertNull($fresh->expiry_date, '售完應清空效期');
+        $this->assertNull($fresh->batch_no, '售完應清空批號');
+    }
+
+    /** 庫存尚未歸 0 → 效期與批號保留（同批貨還在販售）。 */
+    public function test_keeps_expiry_when_stock_remains(): void
+    {
+        $serial = '1234567891';
+        $machine = Machine::factory()->create([
+            'company_id' => $this->company->id,
+            'serial_no' => $serial,
+        ]);
+        $slot = $machine->slots()->create([
+            'slot_no' => '2',
+            'stock' => 5,
+            'max_stock' => 10,
+            'expiry_date' => '2030-12-31',
+            'batch_no' => 'B-001',
+        ]);
+
+        $this->service->recordDispense($this->dispense($serial, '2'));
+
+        $fresh = $slot->fresh();
+        $this->assertEquals(4, $fresh->stock, '庫存應扣為 4');
+        $this->assertEquals('2030-12-31', $fresh->expiry_date->format('Y-m-d'), '未售完應保留效期');
+        $this->assertEquals('B-001', $fresh->batch_no, '未售完應保留批號');
+    }
+}