A 13-year-old boy with ulcerative colitis was admitted to our hospital for the purpose of controlling diarrhea. He had received total colectomy and had been managed by intravenous hyper alimentation because of severe diarrhea (10 times/day). Oral intake had been prohibited except for fluid. Abdominal CT scan incidentally revealed two small calculi in the left kidney, which were left untreated. Two months later, one of them descended and was impacted into the urethra. Transurethral cystolitholapaxy showed the stone composition to be pure ammonium acid urate. Although ammonium acid urate lithiasis is rare in Japan, it should be reminded as a complication of chronic diarrhea secondary to inflammatory bowel disease in children.