Background: Polycystic ovarian syndrome (PCOS) is a common endocrinopathy that accompanied with long term complications. The early diagnosis of this syndrome can prevent it. Objective: The aim was to determine the role of anti-mullerian hormon (AMH) in PCOS diagnosis and to find cut off level of it. Materials and Methods: In this cross sectional study, 117 women between 20-40 years old were participated in two groups: 60 PCOS women (based on Rotterdam criteria consensus) as the case group and 57 normal ovulatory women as the control group. In day 2-4 of cycle, transvaginal sonography was performed and serum hormonal level of AMH, luteinizing hormone (LH), follicle stimulating hormone (FSH), estradiol (E2), testosterone, fasting blood sugar (FBS), thyroid stimulating hormone (TSH), and prolactin (PRL) were measured in all of participants. For all of them score of hirsutism (base on Freeman-Galloway scoring) was determined. Results: There were statistically significant in irregular pattern of menstruation, AMH and FSH level, and presence of hirsutism between two groups. But regarding mean of age, body mass index, plasma level of PRL, TSH, LH, Testosterone, FBS, and E2 differences were not significant. Construction by ROC curve present 3.15 ng/ml as AMH cut off with 70.37% sensitivity and 77.36% specificity in order to PCOS diagnosis. Conclusion: AMH with cut off level of 3.15 ng/ml with sensitivity 70.37% and specificity 77.36% could use for early diagnosis of PCOS patients.