Villous adenomas are common in the gastrointestinal tract but are rare in the urinary tract. Villous adenomas of the urinary tract are identified mostly in the urinary bladder in the current published literature in English. There are only scattered individual case reports showing villous adenoma in the other parts of the urinary tract such as the urethra, ureter, and renal pelvis. Here, we report a fourth case of villous adenoma in the renal pelvis with manifestation of mucus-filled kidney (muconephrosis). A 54-year-old male patient presented with acute urinary retention with mucinuria initially and he finally received nephrectomy. No obvious evidence of recurrence has been noted in the 1-year follow-up.