We have previously reported that a decreased expression level of ICAM-1 in cancer cells frequently led to the development of lymph node metastasis, and suggested that ICAM-1 gene transfection may inhibit lymph node metastasis. In the present study, we investigated whether ICAM-1 gene therapy for the peritoneal metastasis of gastric carcinoma is useful as a new immuno-gene therapy. ICAM-1 gene was transfected into a gastric cancer cell line, OCUM-2MD3 (2MD3), which has a high metastatic ability to the peritoneum. A transfectant cancer cell line, 2MD3/ICAM-1, had high ICAM-1 expression on the cell surface. The adhesion and cytotoxicity abilities of peripheral blood mononuclear cells were significantly increased against 2MD3/ICAM-1 cells in comparison with 2MD3 cells. Mice inoculated with 2MD3/ICAM-1 cells in the peritoneal cavity had a significantly better survival rate than those inoculated with 2MD3 cells (log-rank test, p<0.05). Histologic findings revealed that more mononuclear cells existed around the metastatic nodules in 2MD3/ICAM-1. Although gastric carcinoma frequently causes peritoneal metastasis, no useful therapy for the metastasis of gastric carcinoma has been developed. These findings revealed that ICAM-1 gene transfection to cancer cells could be a useful immuno-gene therapy for the peritoneal metastasis of gastric carcinoma.