We report a case of cecal cancer associated with acute appendicitis. A 74-year-old man admitted with right lower abdominal pain underwent emergency surgery for acute appendicitis. He was treated with anticoagulant drugs, so general anesthesia was selected. An elastic hard mass was palpable in the lower right abdomen. Suspecting a tumor of the ileocecum region, laparotomy was done with a pararectal incision. The appendix was swollen, and a 4 cm diameter tumor was found in the cecum, necessitating ileocecal resection. The histopathological diagnosis was appendicitis catarrhalis with 3.8×4.2 cm cecal cancer, Borr1, well-differentiated adenocarcinoma (ss, ly₁, v₀, n₀, H₀, P₀, stage II). Cecal cancer caused by acute appendicitis is rare. To avoid overlooking cecal cancer, it is important to consider intraoperative exploration.