Acute appendicitis, the major cause of which is obstruction of the appendiceal lumen due to lymphoid hyperplasia. Although acute appendicitis is not common among elderly individuals, appendicitis resulting from appendiceal lumen obstruction due to right-sided colon cancer should always remain a concern in the elderly. Here we report a case involving an 85-year-old female patient presenting clinical features of appendicitis who was ultimately diagnosed with proximal ascending colon cancer and underwent right hemicolectomy. Preoperative computed tomography scanning offered a rapid and reliable image for diagnosis, and the result revealed the highly suspected right-sided colon cancer causing obstruction and acute appendicitis. Thus, right hemicolectomy with lymph node dissection was performed. The pathology report revealed poorly differentiated adenocarcinoma of the proximal ascending colon with a stage of pT3N1a. The appendiceal base was involved by tumor. In this case, appendectomy may increase the risk for poor healing of the appendiceal base and peritoneal seeding, which has been related to poor oncologic outcomes. Accordingly, one-stage curative surgery has been a safe and feasible treatment for right-sided colon cancer concurrent appendicitis.