We present the first reported case of spontaneous ruptured middle colic artery aneurysm in a patient who has concurrent hypervascular tumor which has a potential for rupturing. A 68-year-old Japanese man was admitted with abdominal pain and hypervascular renal tumor which developed in the subcapsular cortex and protruded outward. The next morning after admission, anemia rapidly progressed and severe abdominal pain developed. Emergency laparotomy was performed for a preliminary diagnosis of ruptured hypervascular renal tumor. However, the renal tumor was not ruptured but a ruptured middle colic artery aneurysm was found. The aneurysm measured 3.0 x 2.0 cm in greatest diameter and was resected. Three weeks later, nephrectomy for hypervascular renal tumor was electively performed. Histologically, the tumor was clear cell carcinoma. In the present case, the diagnosis of ruptured middle colic artery was extremely difficult.