In our hospital, one case of colon duplication was found, and was confirmed by radological examination, surgery and pathology. This twenty-one year old female has been suffered from intermittent colicky lower abdominal pain and palpable abdominal mass. During the colon examination, the normal colon filled in retrograde manner, and the single terminal ileum was seen. The anomalous colon filled from the midportion of the descending colon, ended blindly. An intravenous pyelogram and a small bowel series revealed normal kidney, ureter, bladder and small bowel except malrotation of the both kidneys and contrast filled blind end of the duplicated colon located near the pelvic area of the right kidney. The patient was in excellent physical condition, and after admission to the hospital, a operation was performed. The findings were exactly as previously discribed.