A 10 year old boy with mucinous carcinoma of rectum is a rare case at this age. Here the patient presented with constipation, mucus in stool & abdominal pain since one month. He got consultation from several physicians & went through sonology of whole abdomen several times. There he was missed diagnosed as a case of pyloric stenosis. We came to a probable diagnosis by doing simple digital rectal examination which seemed to be a hard rectal swelling. The diagnosis was established by colonoscopy followed by biopsy. Carcinoma rectum must be considered as a differential diagnosis if patient presents with altered bowel habit, per rectal bleeding, abdominal pain in conjunction with weight loss.