A 65-year-old man was diagnosed with HER2-positive gastric cancer considered unresectable owing to multiple distant lymph node metastases. After long-term chemotherapy, the original lesion disappeared, while peri-gastric lymph node metastases remained. Therefore, we performed lower mediastinal lymph node dissection, total gastrectomy with regional lymph node dissection (D2) and cholecystectomy. Pathological evaluation indicated that the main gastric tumor showed complete response, while there was metastasis in the No.3 lymph nodes, which showed HER2 positivity (3+). At present, the patient has received Xeloda plus trastuzumab and remains relapse-free 5 months after conversion surgery.