Satisfactory therapeutic effects are rarely obtained with oral chemotherapy for gastric cancer. We have experienced successful treatment for synchronous hepatic metastasis of gastric cancer with 5'-DFUR and Lentinan. The patient was a 78-year-old female, diagnosed as having gastric cancer with multiple hepatic metastases, who underwent gastrectomy. Immunohistochemistry of the resected specimens with anti-thymidine phosphorylase (dThdPase) antibody yielded positive results for dThdPase in the primary tumor as well as the hepatic metastases. Two months after surgery, administration of 400 mg of 5'-DFUR per day and 2 mg i.v. of Lentinan every other week was started. Four months after discharge, carcinoembryonic antigen (CEA) in plasma showed an abrupt logarithmic decline. Furthermore, a 99% reduction in hepatic metastases was demonstrated by abdominal CT. At present, 22 months after surgery, the patient is managed on an outpatient basis with no complaints of any side effects. Immunochemotherapy using 5'-DFUR and Lentinan may be effective against gastric malignancies expressing dThdPase activity.