A 70-year-old man was referred to our hospital with ascending colon cancer (cT3N1M0, Stage IIIa), which was found during examinations following a positive fecal occult blood test. The patient was also diagnosed with early gastric cancer (cT1a, N0, M0, Stage IA)during a preoperative gastroscopy examination. A laparoscopically assisted right colectomy and D3 lymphadenectomy was performed for the ascending colon cancer. The postoperative pathological diagnosis was Stage IIIb (pT3N2), he was administered in combination with capecitabine plus oxaliplatin (CapeOX) as adjuvant chemotherapy before the treatment for the colon cancer. After 6 months of adjuvant chemotherapy, we were unable to detect any gastric lesions at the same location using gastroscopy, and so diagnosed a clinical complete response. A follow-up gastroscopy 6 months later showed the same findings. The patient has had no recurrence of gastric cancer for 18 months after the initial operation. He will continue to be followed up closely using gastroscopy. In this case, CapeOX as adjuvant chemotherapy for advanced colon cancer was also effective for early gastric cancer.