Objective: In our study, we aimed to investigate the effects of Jun N-terminal kinase inhibitor (SP600125) on fibrosis and inflammation in rats with polycystic ovary syndrome (PCOS). Method: 50 Wistar-albino rats were divided into five groups (n=10 each): control group, sham group, PCOS group, SP600125+ PCOS group and SP600125 group. In the estradiol valerate (EV)-treated group in which PCOS was injected with a single 4 mg/kg i.p. of EV in 0.2 ml sesame oil and the rats were sacrificed on day 60. The estradiol valerate (EV)-treated + SP600125-treated group was injected with a single 4 mg/kg i.p. of EV in 0.2 ml sesame oil. As of day 60, the treatment group was additionally given 15 mg/kg i.p. of SP600125 once daily for 4 consecutive days and the rats were sacrificed on day 65. Histopathological findings (ovarian morphology, edema, inflammatory cell infiltration, vascular congestion and hyperemia) and collagen type IV immunoexpression were assessed. Results: The SP600125+ PCOS group showed a significant level of improvement in ovarian follicle morphology, edema, inflammatory infiltrate, vascular congestion and hyperemia as compared with the PCOS group. Furthermore, collagen type IV immunoexpression showed a significant reduction in staining intensity on the theca cell layer and ovary stroma as compared to the PCOS group. Conclusion: This study demonstrates the therapeutic effect of SP600125 in the prevention of PCOS in an experimental model.