The urachus is an embryological remnant of the allantois extending from the umbilicus to the urinary bladder apex and it uncommonly persists in adults.^[1] Urachal malignancy is a rare adn represents less than one percent of bladder neoplasm.^[2] Here we present a case report of 64 year old male presented to surgery opd with complain of lower abdominal pain since 1 year. Patient had no irritative urinary symptoms and no history of loss of weight and appetite. On examination there was single mass located in infraumbilical region of size 6 x 5 cm². CT scan suggested 4.8 x 8 x 6.4 cms sized multiloculated, predominantly hypodense with lobulated margin extending from dome of the bladder to umbilicus superiorly, Lesion shows high density fluid and linear calcifications within it possibility of mucinous cystadenoma of remenant of urachus. Histology revealed mucinous cystadenoma of undetermined malignant potential, rarest histological variety and difficult to diagnose on basis of mucin histochemistry and immunohistology. Six months follow–up did not show any local tumour recurrence.