A 62-year-old man was diagnosed with gastric cancer and underwent distal gastrectomy, and D1+b lymph node dissection. He was diagnosed postoperatively with T1b (sm2) N0M0, StageⅠA gastric adenocarcinoma and did not receive any adjuvant chemotherapy after surgery. One year and 6 months after gastrectomy, blood analysis indicated high levels of carcinoembryonic antigen (CEA 262.1 ng/mL) while abdominal computed tomography (CT) revealed multiple liver tumors (S7: 15 mm, S7/8: 20 mm). The patient was diagnosed with metachronous multiple liver metastases from gastric cancer. Chemotherapy, combined with molecular targeted therapy (S-1 plus cisplatin [CDDP] plus trastuzumab), was administered because of overexpression of the human epidermal growth factor receptor 2 (HER2) protein in the primary tumor as assessed by immunohistochemistry, the CEA levels decreased immediately after 2 cycles of the chemotherapy, and the liver metastases shrank markedly with no evidence of new lesions on abdominal CT. However, after treatment, Grade 3 neutropenia and diarrhea were observed. Chemotherapy was suspended and hepatic resection was performed. After hepatic resection, the liver tumors were histologically evaluated as Grade 2 metastatic gastric adenocarcinoma, and the HER2 expression of remnant carcinoma cells was established. The patient has been in good health and remained free of recurrences in the 2 years and 3 months after the liver resection. Surgery with preoperative chemotherapy (S-1 plus CDDP plus trastuzumab) can be an effective treatment for liver metastasis from HER2-positive gastric cancer.