Polycystic ovary syndrome (PCOS) is the most common etiology of menstrual disorders and hyperandrogenism, and The understanding of PCOS has advanced significantly. However, a fully convincing animal model for study of polycystic ovaries, or of PCOS, has not been established in the mouse. In the present study, polycystic ovary (PCO) was induced by a single intraperitoneal injection of testosterone propionate (TP; 0.1 mg, dissolved in sesame oil) in female mice at 4–5 days of age. The mice exhibited either constant estrus or diestrus for 5 weeks after TP administration, and this resulted in anovulatory polycystic ovaries. These ovaries contained multiple large follicles and no corpus luteum. The morphology and ovulatory failure were similar to those of the PCOs of humans and other animals. In these ovaries, we found that only the oocytes in the secondary follicles had the following cytological changes: first meiotic division metaphase, second meiotic division metaphase, parthenogenesis and fragmentation. This mouse model has potential for application in studies of folliculogenesis and the mechanism of androgen-induced PCO.