A case of bizarre leiomyoblastoma (BL) of the cervix uteri which developed in a 44-year-old premenopausal woman was reported. The tumor was found as a cervical polyp by routine pelvic examination. Histologically, it was composed of epithelioid and bizarre, often multinucleated, giant tumor cells without elevated mitotic counts and necrosis. Electronmicroscopically, abundant myofilaments in epithelioid tumor cells were observed. Immunoreactive desmin, CPK-MM (creatinine kinase mm-isozyme), and myosin could be demonstrated in most of the epithelioid tumor cells. These immunohistochemical findings seemed to reflect on the differentiation of the tumor cells to smooth muscle and provide a reliable evidence for the smooth muscle origin. The histogenesis and relationship between the histopathological findings and clinical behaviour of uterine BL were also discussed.