Uterine leiomyosarcoma is a rare uterine malignancy that arises from the smooth muscle of uterine wall. Presenting symptoms may be vague and mimic other benign uterine conditions. They are notoriously aggressive with poor prognosis. We report a case of a 35-year-old female, who presented with abdominal distension with pain and vomiting. A non-tender mass measuring 14X12 cms was felt on palpation in the same region. CT scan revealed a large, relatively well defined, hypodense pelvic mass in retro-uterine pouch. Patient underwent exploratory laparotomy with primary resection of tumour with pan-hysterectomy with pelvic lymph node resection. Histopathologically, it was diagnosed as pleomorphic sarcoma probably leiomyosarcoma of uterus which showed immunostain Smooth Muscle Antigen (SMA) positive and Epithelial Membrane Antigen (EMA) negative. It was Estrogen Receptor(ER) negative. The rarity as well as pathological diversity makes this study beneficial and this definitive reporting will be helpful in diagnosis of smooth muscle tumours with challenging histologic features.