diff --git a/database/factories/StockFactory.php b/database/factories/StockFactory.php
new file mode 100644
index 0000000..53b753e
--- /dev/null
+++ b/database/factories/StockFactory.php
@@ -0,0 +1,31 @@
+<?php
+
+namespace Database\Factories;
+
+use App\Models\Tenants\Stock;
+use Illuminate\Database\Eloquent\Factories\Factory;
+
+/**
+ * @extends Factory<Stock>
+ */
+class StockFactory extends Factory
+{
+    protected $model = Stock::class;
+
+    public function definition(): array
+    {
+        return [
+            'item_code' => 'ITM-'.strtoupper(fake()->unique()->bothify('???###')),
+            'item_name' => fake()->word().' 부품',
+            'item_type' => 'raw_material',
+            'unit' => 'EA',
+            'stock_qty' => 0,
+            'safety_stock' => 10,
+            'reserved_qty' => 0,
+            'available_qty' => 0,
+            'lot_count' => 0,
+            'status' => 'out',
+            'location' => 'A-01',
+        ];
+    }
+}
diff --git a/database/factories/StockLotFactory.php b/database/factories/StockLotFactory.php
new file mode 100644
index 0000000..a4a5d00
--- /dev/null
+++ b/database/factories/StockLotFactory.php
@@ -0,0 +1,28 @@
+<?php
+
+namespace Database\Factories;
+
+use App\Models\Tenants\StockLot;
+use Illuminate\Database\Eloquent\Factories\Factory;
+
+/**
+ * @extends Factory<StockLot>
+ */
+class StockLotFactory extends Factory
+{
+    protected $model = StockLot::class;
+
+    public function definition(): array
+    {
+        return [
+            'lot_no' => 'LOT-'.fake()->unique()->numerify('######'),
+            'fifo_order' => 1,
+            'receipt_date' => now(),
+            'qty' => fake()->numberBetween(10, 100),
+            'reserved_qty' => 0,
+            'available_qty' => 0,
+            'unit' => 'EA',
+            'status' => 'available',
+        ];
+    }
+}
diff --git a/tests/Feature/Inventory/StockApiTest.php b/tests/Feature/Inventory/StockApiTest.php
new file mode 100644
index 0000000..f0fc4d4
--- /dev/null
+++ b/tests/Feature/Inventory/StockApiTest.php
@@ -0,0 +1,272 @@
+<?php
+
+namespace Tests\Feature\Inventory;
+
+use App\Models\Tenants\Stock;
+use App\Models\Tenants\StockLot;
+use App\Models\Tenants\StockTransaction;
+use App\Services\StockService;
+use Tests\TestCase;
+
+class StockApiTest extends TestCase
+{
+    protected function setUp(): void
+    {
+        parent::setUp();
+        $this->setUpAuthenticatedUser();
+    }
+
+    // ==================== API 엔드포인트 ====================
+
+    public function test_재고_목록_조회(): void
+    {
+        $this->createStockWithLot(50);
+
+        $response = $this->api('get', '/api/v1/stocks');
+
+        $this->assertApiPaginated($response);
+    }
+
+    public function test_재고_통계_조회(): void
+    {
+        // 정상 재고
+        $this->createStockWithLot(50, 10);
+        // 부족 재고
+        $this->createStockWithLot(5, 10);
+        // 빈 재고
+        $this->createStock(0, 10);
+
+        $response = $this->api('get', '/api/v1/stocks/stats');
+
+        $response->assertStatus(200)
+            ->assertJsonStructure(['success', 'data']);
+    }
+
+    public function test_품목유형별_통계_조회(): void
+    {
+        $this->createStockWithLot(30, 10, 'raw_material');
+        $this->createStockWithLot(20, 5, 'purchased_part');
+
+        $response = $this->api('get', '/api/v1/stocks/stats-by-type');
+
+        $response->assertStatus(200)
+            ->assertJsonStructure(['success', 'data']);
+    }
+
+    public function test_재고_상세_존재하지_않는_품목_404(): void
+    {
+        // Stock API는 Item 기준 조회 → 존재하지 않는 Item ID는 404
+        $response = $this->api('get', '/api/v1/stocks/999999');
+
+        $response->assertStatus(404);
+    }
+
+    public function test_미인증_요청시_401(): void
+    {
+        $response = $this->withHeaders([
+            'X-API-KEY' => $this->apiKey,
+            'Accept' => 'application/json',
+        ])->getJson('/api/v1/stocks');
+
+        $response->assertStatus(401);
+    }
+
+    // ==================== FIFO 핵심 로직 ====================
+
+    public function test_FIFO_입고시_LOT_생성_및_순서_할당(): void
+    {
+        $stock = $this->createStock(0, 10);
+
+        // LOT 1 생성 (fifo_order = 1)
+        $lot1 = $this->addLot($stock, 30, 1);
+        // LOT 2 생성 (fifo_order = 2)
+        $lot2 = $this->addLot($stock, 20, 2);
+
+        $stock->refresh();
+        $stock->refreshFromLots();
+
+        $this->assertEquals(50, $stock->stock_qty);
+        $this->assertEquals(50, $stock->available_qty);
+        $this->assertEquals(2, $stock->lot_count);
+        $this->assertEquals('normal', $stock->status);
+    }
+
+    public function test_FIFO_차감시_오래된_LOT부터_감소(): void
+    {
+        $stock = $this->createStock(0, 10);
+        $lot1 = $this->addLot($stock, 30, 1); // 먼저 입고
+        $lot2 = $this->addLot($stock, 20, 2); // 나중 입고
+        $stock->refreshFromLots();
+
+        // FIFO 차감: 25개 요청 → LOT1에서 25개 차감
+        $service = app(StockService::class);
+        $service->setContext($this->tenant->id, $this->user->id);
+        $result = $service->decreaseFIFO($stock->item_id, 25, 'shipment', 1);
+
+        $lot1->refresh();
+        $lot2->refresh();
+
+        // LOT1: 30 → 5 (25 차감)
+        $this->assertEquals(5, $lot1->qty);
+        // LOT2: 변화 없음
+        $this->assertEquals(20, $lot2->qty);
+    }
+
+    public function test_FIFO_차감시_LOT_걸침_처리(): void
+    {
+        $stock = $this->createStock(0, 10);
+        $lot1 = $this->addLot($stock, 10, 1);
+        $lot2 = $this->addLot($stock, 20, 2);
+        $stock->refreshFromLots();
+
+        // 15개 차감 → LOT1(10) 전부 + LOT2(5) 일부
+        $service = app(StockService::class);
+        $service->setContext($this->tenant->id, $this->user->id);
+        $result = $service->decreaseFIFO($stock->item_id, 15, 'shipment', 2);
+
+        $lot1->refresh();
+        $lot2->refresh();
+
+        $this->assertEquals(0, $lot1->qty);
+        $this->assertEquals(15, $lot2->qty);
+    }
+
+    public function test_재고_부족시_예외_발생(): void
+    {
+        $stock = $this->createStockWithLot(10);
+
+        $service = app(StockService::class);
+        $service->setContext($this->tenant->id, $this->user->id);
+
+        $this->expectException(\Exception::class);
+        $service->decreaseFIFO($stock->item_id, 999, 'shipment', 3);
+    }
+
+    // ==================== 예약/해제 ====================
+
+    public function test_수주_확정시_재고_예약(): void
+    {
+        $stock = $this->createStock(0, 10);
+        $lot1 = $this->addLot($stock, 50, 1);
+        $stock->refreshFromLots();
+
+        $service = app(StockService::class);
+        $service->setContext($this->tenant->id, $this->user->id);
+        $service->reserve($stock->item_id, 20, 100); // orderId=100
+
+        $lot1->refresh();
+        $stock->refresh();
+
+        $this->assertEquals(20, $lot1->reserved_qty);
+        $this->assertEquals(30, $lot1->available_qty);
+        $this->assertEquals(20, $stock->reserved_qty);
+    }
+
+    public function test_수주_취소시_예약_해제(): void
+    {
+        $stock = $this->createStock(0, 10);
+        $lot1 = $this->addLot($stock, 50, 1);
+        $stock->refreshFromLots();
+
+        $service = app(StockService::class);
+        $service->setContext($this->tenant->id, $this->user->id);
+
+        // 예약
+        $service->reserve($stock->item_id, 20, 100);
+        // 해제
+        $service->releaseReservation($stock->item_id, 20, 100);
+
+        $lot1->refresh();
+        $stock->refresh();
+
+        $this->assertEquals(0, $lot1->reserved_qty);
+        $this->assertEquals(50, $lot1->available_qty);
+        $this->assertEquals(0, $stock->reserved_qty);
+    }
+
+    // ==================== 거래 이력 ====================
+
+    public function test_차감시_거래이력_기록(): void
+    {
+        $stock = $this->createStockWithLot(50);
+
+        $service = app(StockService::class);
+        $service->setContext($this->tenant->id, $this->user->id);
+        $service->decreaseFIFO($stock->item_id, 10, 'shipment', 5);
+
+        $transaction = StockTransaction::where('stock_id', $stock->id)
+            ->where('type', StockTransaction::TYPE_OUT)
+            ->first();
+
+        $this->assertNotNull($transaction);
+        $this->assertEquals(-10, $transaction->qty);
+        $this->assertEquals('shipment', $transaction->reason);
+    }
+
+    // ==================== Stock 상태 자동 계산 ====================
+
+    public function test_재고_상태_자동_계산(): void
+    {
+        // 정상: stock_qty > safety_stock
+        $stock = $this->createStockWithLot(50, 10);
+        $this->assertEquals('normal', $stock->calculateStatus());
+
+        // 부족: 0 < stock_qty <= safety_stock
+        $stock2 = $this->createStockWithLot(5, 10);
+        $this->assertEquals('low', $stock2->calculateStatus());
+
+        // 없음: stock_qty = 0
+        $stock3 = $this->createStock(0, 10);
+        $this->assertEquals('out', $stock3->calculateStatus());
+    }
+
+    // ==================== 헬퍼 ====================
+
+    private function createStock(int $qty, int $safetyStock = 10, string $itemType = 'raw_material'): Stock
+    {
+        return Stock::create([
+            'tenant_id' => $this->tenant->id,
+            'item_id' => rand(100000, 999999),
+            'item_code' => 'ITM-'.uniqid(),
+            'item_name' => '테스트 품목',
+            'item_type' => $itemType,
+            'unit' => 'EA',
+            'stock_qty' => $qty,
+            'safety_stock' => $safetyStock,
+            'reserved_qty' => 0,
+            'available_qty' => $qty,
+            'lot_count' => 0,
+            'status' => $qty > $safetyStock ? 'normal' : ($qty > 0 ? 'low' : 'out'),
+            'location' => 'A-01',
+            'created_by' => $this->user->id,
+            'updated_by' => $this->user->id,
+        ]);
+    }
+
+    private function createStockWithLot(int $qty, int $safetyStock = 10, string $itemType = 'raw_material'): Stock
+    {
+        $stock = $this->createStock($qty, $safetyStock, $itemType);
+        $this->addLot($stock, $qty, 1);
+        $stock->refreshFromLots();
+
+        return $stock;
+    }
+
+    private function addLot(Stock $stock, int $qty, int $fifoOrder): StockLot
+    {
+        return StockLot::create([
+            'tenant_id' => $this->tenant->id,
+            'stock_id' => $stock->id,
+            'lot_no' => 'LOT-'.uniqid(),
+            'fifo_order' => $fifoOrder,
+            'receipt_date' => now(),
+            'qty' => $qty,
+            'reserved_qty' => 0,
+            'available_qty' => $qty,
+            'unit' => 'EA',
+            'status' => 'available',
+            'created_by' => $this->user->id,
+            'updated_by' => $this->user->id,
+        ]);
+    }
+}