Purpose: This study was designed to investigate the effects of Cyperi Rhizoma (CR) on changes in weights morphological and histopathological observations in Polycystic Ovary(PCO) rats. Methods: PCO was induced by single intramuscular injection with EV(2mg) in female rats. Normal group(n=8) were injected with sesame oil and orally administrated distilled water for five weeks. PCO control group(n=8) were injected with EV and orally administrated distilled water for five weeks. CR treated group(n=8) were injected with EV and orally administrated CR for five weeks. Then we measured weight of body, ovaries. The histopathology changes of ovaries, and the expression of nerve growth factor(NGF) were also evaluated. Results: Single injection of EV induced suppression of weight gain, formation of cysts, increase of NGF expression. Oral administration of CR prevent suppression of weight gain shown in control group. In addition CR group showed upward tendency of ovarian size. Formation of cystic follicles induced by EV injection is suppressed by CR treatment. In additon, CR treatment lowered expression levels of nerve growth factor(NGF), which were elevated by induction of PCOS. Conclusion: These results suggest that CR can be used for patients with PCOS to prevent formation of cystic follicles and malfunction of ovary. And also suggest that the related mechanisms are involved in suppression of NGF expression.