We report a surgical case of descending colon cancer with abdominal wall abscess. A 72-year-old man was admitted to a hospital because of left lower abdominal mass with slight pain. An abdominal CT showed a left lower abdominal wall abscess adjacent to the descending colonic wall thickening. We diagnosed an abdominal wall abscess due to descending colon cancer or colon diverticulitis. The abscess was drained under local anesthesia releasing foul-smelling pus and air. After abscess drainage and general improvement in his condition, we conducted subtotal colectomy with lymph node dissection and excision of abdominal wall abscess cavity. Pathological findings indicated moderately differentiated adenocarcinoma of the descending colon (pT4, pN0, sH0, sP0, sM0, fStage II). The carcinoma had invaded the abdominal wall and transverse colon, but the cancer cells were not shown in the abdominal wall abscess cavity. In abdominal wall abscess treatment, colon cancer should be considered as a potential underlying cause. CT proved useful for assessing the status of the tumor and the abscess. We conducted a radical operation for descending colon cancer after the drainage for abdominal wall abscess.