We report a case of peritoneal cancer dissemination and cytological appearance of cancer cells with Type 4 gastric cancer. Treatment with unichemotherapy and combination chemotherapy with TS-1 proved successful. The patient was a 58-year-old female,who complained of abdominal pain. She was diagnosed as unresectable Type 4 gastric cancer, T 3 NxH 0 P 1 CY 1 M 0, Stage IV (cytology: Class V). Thirteen days after surgery, chemotherapy with TS-1 (80 mg/body/day, 4 weeks) at 2-week intervals in 1 course was performed. However, due to side effects with marrow restraint of grade 1, we changed to the following chemotherapy regimen: TS-1 (80 mg/body/day, 2 weeks) at 4-week intervals as 1 course (23 courses in total). After 16 courses, a partial response (PR) was noted. As additional therapy to recover tumor marker (CA19-9) after 21 courses, combination chemotherapy with TS-1 (80 mg/body/day, 2 weeks) and CDDP (25 mg/body/day, day 1, 8, 15 drip infusion) was performed as one course. This chemotherapy was then performed in 3 courses and tumor markers did not deteriorate, so we changed docetaxel (DOC) (50 mg/body/day(day 1)) to CDDP, and tumor markers returned to the normal value. No recurrence and no side effects appeared (hematological or non-hematological) during this combination chemotherapy.