A 77-year-old man presented to our hospital with diarrhea and weight loss. Upper gastrointestinal endoscopy revealed advanced Type 3 gastric cancer measuring 40 mm in the lower greater curvature of the stomach. Biopsy from a gastric tumor revealed moderately differentiated tubular adenocarcinoma overexpressing HER2. Abdominal contrast-enhanced computed tomography(CT)showed multiple liver metastases in S3 and S5. We diagnosed HER2-positive gastric cancer with liver metastasis. Systemic chemotherapy was administrated, with a total of 13 courses of combination therapy with S-1, oxaliplatin and trastuzumab. After chemotherapy, the primary tumor was significantly reduced and liver metastases were almost undetectable. Laparoscopic distal gastrectomy and partial hepatectomy were performed as conversion surgery. The patient was discharged on the 9th day without any postoperative complications. Postoperative pathological findings showed no residual tumor in either gastric and hepatic specimens, and the therapeutic effect of chemotherapy was diagnosed as pathological complete response. We report a case of HER2-positive advanced gastric cancer with multiple liver metastases that achieved a pathologically complete response to chemotherapy followed by conversion surgery. Laparoscopic surgery would be one of an effective option for conversion surgery.