Soft tissue sarcomas (STSs) are a heterogeneous group of rare neoplasms originating from the embryonic mesoderm and mesenchymal cells. Primary peritoneal sarcomas have been reported as leiomyosarcoma, liposarcoma and carcinosarcoma. However, primary peritoneal spindle cell sarcoma has never been reported in the literature. Herein, we report on a 38-year-old woman with massive ascites diagnosed as primary peritoneal spindle cell sarcoma. Following doxorubicin and ifosfamide chemotherapy, her symptoms improved and ascites regressed. Other primary peritoneal sarcomas rarely cause massive ascites. We suggest that in patients presenting with massive exudative ascites associated with malignancy, primary peritoneal sarcomas should be also considered in the differential diagnosis.