Although glandular and stromal proliferations of prostate are very common in adult men, neoplastic proliferations of prostatic stroma are distinctly uncommon. These tumors are now grouped as Prostatic Stromal Proliferations of Uncertain Malignant Potential (PSPUMP). Phyllodes tumor of the prostate is a rare neoplasm in this group with cellular, sarcomatoid stroma and benign hyperplastic glands. It is a locally expansile tumor with clinical course varying from benign to aggressive. We report a case of a 45-year-old man presented with retention of urine and abdominal lump. On laparotomy it was a huge tumor of 4 kg and was histologicaly characterized by cellular pleomorphic stroma and hyperplastic epithelium. Immunohistochemistry demonstrated prostate specific antigen in the glands. It was diagnosed as cystosarcoma phyllodes tumor of prostate. This is extremely uncommon tumor similar in histology to that of breast and it′s clinical course varies with the grade. The patient was without recurrence one year after surgery.