Desmoplastic small round cell tumor (DSRCT) is rare and highly malignant mesenchymal neoplasm found in the abdominal cavity that associated with prominent stromal desmoplasia and polyphenotypic differentiation. We report a case of DSRCT that occured in pelvic cavity in young woman. Pelvis CT scan and MRI documented about 10 cm sized heterogenous, cystic and solid mass, multiple peritoneal nodules and massive ascites in pelvic cavity as well as an elevated CA-125 level at presentation. A 31-year-old female presented to another institution with a pelvic mass and abdominal discomfort. During tumor reductive surgery the both ovary, omentum, small bowel, large bowel and pelvic peritoneum were found to be involved. Morphology, immunohistochemistry, and molecular cytogenetics were consistent with DSRCT. Despite tumor reductive surgery the patient died at 18 days after initial diagnosis. This is a case of DSRCT mimicking ovarian cancer and an elevated CA-125 level.