We report 2 cases of signet ring cell carcinoma of the appendix and colon. Case 1: A 61-year-old man was admitted for lower abdominal pain. Colonoscopy revealed an elevated lesion in the orifice of the appendix. Signet ring cell carcinoma was diagnosed on biopsy. The surgical findings showed multiple peritoneal dissemination nodules, while the primary tumor was unresectable owing to extensive invasion into the retroperitoneum. The histopathological findings were signet ring cell carcinoma, T4b (retroperitoneum), NX, P3, Stage Ⅳ. Although the patient received 14 courses of treatment with S-1 as postoperative chemotherapy, he died of his illness at 32 postoperative months. Case 2: A 76-year-old man was admitted for abdominal pain. Perforation of the lower gastrointestinal tract was diagnosed on abdominal CT, and an emergency operation was performed. The surgical findings demonstrated a large number of peritoneal dissemination nodules, cecal invasion of a sigmoid tumor, and perforation of the ascending colon. The primary tumor was thought to be unresectable, and the perforated segment was resected. The histopathological findings were signet ring cell carcinoma, T4b (cecum), NX, P3, Stage Ⅳ. Although 11 courses of treatment using FOLFIRI+Bev were administered as postoperative chemotherapy, the patient died of his illness at 26 postoperative months.