A 67-year-old woman was diagnosed as having advanced gastric cancer(poorly differentiated adenocarcinoma)with multiple liver metastases. She had received combined S-1 plus cisplatin chemotherapy as first-line treatment and weekly paclitaxel chemotherapy as second-line treatment, however, both had eventually proved ineffective. Because the gastric cancer was HER2-positive, she was treated with trastuzumab plus capecitabine plus cisplatin(XP)chemotherapy as third-line treatment. The primary lesion and liver metastatic lesions were confirmed to show remarkable regression. The ToGA trial revealed increased efficacy of trastuzumab in first-line treatment of cancers showing high expression levels of the HER2- protein. This case suggested the increased efficacy of trastuzumab in third-line treatment. Neutropenia and hand foot syndrome of grade 2 were all reported adverse events. She could receive trastuzumab plus XP chemotherapy safely by dose reduction or dormancy temporarily of capecitabine.