The purpose of the study was to investigate the effects of Exendin-4 on polycystic ovary syndrome (PCOS) in rats in chronic mild stress medium. For establishing the PCOS model, dehydroepiandrosterone (DHEA) (6mg/100g) in 0.2ml sesame oil was injected subcutaneously to 21-day old rats (n = 67). In addition, 0.2ml sesame oil was injected subcutaneously to the rats in groups involving solution injection only. At the initial stage of the study, the rats were grouped as control, solution and PCOS, whereas stress and Exendin-4 groups were also added in the second stage of the study. In PCOS groups, Exendin-4 was applied intraperitoneally (10 mu g/kg/day) in mild chronic stress medium for four weeks. The results revealed that weight, fasting blood glucose, fasting blood insulin and HOMA-IR levels in the rats with PCOS were significantly higher than in the other groups; also, corticosterone levels of stress groups were significantly higher than in the other groups. In addition, harmful effects of PCOS on ovarian tissues were observed in histological examinations. However, after Exendin-4 application in PCOS groups, weight, fasting blood glucose, fasting blood insulin, HOMA-IR and LH/FSH levels were decreased, whereas Exendin-4 application in PCOS group treated with stress was not as effective as the application of Exendin-4 on rats with PCOS. Exendin-4 application also increased the number of healthy follicles in PCOS group, whereas there was no change in the number of healthy follicles in PCOS+Stress group.