Although the treatment of gastric cancer improves the clinical outcomes, the survival of gastric cancer patients with peritoneal metastasis is still very poor. Effective drugs against peritoneal metastasis, coupled with new therapeutic modalities, are needed to improve the prognoses of these patients. Paclitaxel and TS-1 are candidate drugs for peritoneal metastasis, and intraperitoneal chemotherapy and targeted therapy are potential new therapeutic modalities. Two phase II studies using TS-1 and intraperitoneal and systemic paclitaxel for gastric cancer patients with peritoneal metastasis showed respectable survival results. In addition, peritoneal metastatic lesions showed high levels of epithelial cellular adhesion molecule (ECAM) and very low levels of human epidermal growth factor receptor 2 (HER2), thus indicating that an anti-ECAM monoclonal antibody, catumaxomab, would be effective against gastric cancer-derived peritoneal metastasis. Although catumaxomab and intraperitoneally administered paclitaxel are not generally used in Japan at present, these treatment strategies might therefore be effectively used in Japan in the near future.