A 78-year-old man was diagnosed as HER2-positive unresectable advanced gastric cancer(cT4aN3M1[LYM], Stage Ⅳ). After 2 courses of first-line chemotherapy(S-1 plus oxaliplatin plus trastuzumab), PR was achieved. The treatment could not be continued due to adverse events after 5 courses, thus second-line chemotherapy was conducted. Corresponding to the physical condition. The third-line chemotherapy was also introduced. However, we clinically judged PD because of amount of ascites and chemotherapy was terminated. After that, he has survived for more than 2 years without chemotherapy, and endoscopy and CT showed the disappearance of the tumor, metastatic lymph nodes, and ascites at 41 months after diagnosis. Looking back on the changes in tumor markers, it was possible that he had already achieved CR at the first-line chemotherapy.