diff --git a/app/Services/ReceivingService.php b/app/Services/ReceivingService.php
index 2b2c78ca..4948f23b 100644
--- a/app/Services/ReceivingService.php
+++ b/app/Services/ReceivingService.php
@@ -427,16 +427,29 @@ private function generateReceivingNumber(int $tenantId): string
 
     /**
      * LOT번호 자동 생성
+     *
+     * 5130 레거시 차용: YYMMDD-NN (일별 시퀀스, 01부터 시작)
+     * 개선: 파일 기반 → DB 기반 (테넌트별 격리, 동시성 안전)
      */
     private function generateLotNo(): string
     {
-        $now = now();
-        $year = $now->format('y');
-        $month = $now->format('m');
-        $day = $now->format('d');
-        $seq = str_pad(rand(1, 99), 2, '0', STR_PAD_LEFT);
+        $tenantId = $this->tenantId();
+        $prefix = now()->format('ymd'); // 예: 260317
 
-        return "{$year}{$month}{$day}-{$seq}";
+        $lastReceiving = Receiving::query()
+            ->where('tenant_id', $tenantId)
+            ->where('lot_no', 'like', $prefix.'-%')
+            ->orderBy('lot_no', 'desc')
+            ->first(['lot_no']);
+
+        if ($lastReceiving) {
+            $lastSeq = (int) substr($lastReceiving->lot_no, -2);
+            $newSeq = $lastSeq + 1;
+        } else {
+            $newSeq = 1;
+        }
+
+        return $prefix.'-'.str_pad($newSeq, 2, '0', STR_PAD_LEFT);
     }
 
     /**