A38 -year-old man complaining of abdominal pain was diagnosed with small intestinal cancer. Small intestinal endoscopy and PET-CT showed a primary jejunal cancer and five peritoneal metastases. Partial resection of the jejunum with three metastases was performed, but the others were unresectable. After surgery, FOLFOX chemotherapy was adapted. Follow-up pelvic CT showed a remarkable reduction of tumor size during FOLFOX chemotherapy after 4 courses, and follow-up PET-CT showed no tumor intake FDG after 10 courses. We judged him to be a complete response and stopped chemotherapy. After 7 months, the patient's level of tumor markers elevated, and there was recurrence. We resumed FOLFOX, and the chemotherapy for this patient is still being continued.