An enteric duplication is a relatively common congenital anomaly, which is rarely complicated by infection. We report the radiologic findings including ultrasound, barium enema and computed tomography (CT) of an infected colonic duplication that was confirmed by pathology. This case demonstrated a complex hypoechoic cystic mass with a thick wall and septa in the left lower quadrant of abdomen and increased the color flow on the Color Doppler ultrasonography. On CT images, the cystic mass contained multiple enhancing septa, infiltrated to the mesocolon and displaced the adjacent bowels. On exploration, a large cystic mass with an abscess attached to the mesocolic border adhering to the small bowel was found.