Surgical excision of both primary and metastatic tumors is the recommended therapy for gastric cancer. There are many cases of multiple metastasis to lymph nodes, disseminated metastasis of peritoneum, and post-operative systemic metastasis for which no surgical treatment is available. Cancer gene therapy is one of the promising new techniques. We injected the suicide gene, herpes simplex virus thymidine kinase (HSV-tk), directly into the tumor using gastrofiberscopy. Following GCV treatment caused tissue degeneration at the injection site and lymph nodes. These findings show that suicide gene therapy for gastric cancer may be effective for a metastatic tumor along with the primary tumor.