A 54-year-old man was referred to our hospital for close examination and treatment of an advanced gastric cancer. Gastrointestinal endoscopic examination showed a type 3 tumor, which was diagnosed as well-differentiated adenocarcinoma, and computed tomography showed multiple enlarged liver metastases in both the lobes. He underwent gastrojejunostomy and was treated with S-1 and cisplatin combination chemotherapy. However, after 4 courses of chemotherapy, progression of disease occurred. Because the human epidermal growth factor receptor type 2(HER2) test was positive, we started trastuzumab and paclitaxel combination chemotherapy as a second-line treatment. After administration of 7 courses of trastuzumab and 5 courses of paclitaxel, the primary lesion and multiple liver metastases were greatly reduced. Trastuzumab and paclitaxel combination chemotherapy appears to be an effective treatment for HER2-positive advanced gastric cancer.