Introduction: PCOS prevalence is 5-10 percent among reproductive age women in worldwide. It is caused by imbalance of sex hormones which ultimately leads to menstrual irregularities, infertility, anovulation and other metabolic disturbances. Most women with chronic anovulation is caused by polycystic ovary syndrome [PCOS] The Rotterdam criteria is useful diagnostic tool for PCOS. In Mongolia there is almost no study on PCOS related infertility and there are increasing trend infertility among reproductive aged women with PCOS, lead us to conduct the study. Objective: The aim of this study was to estimate incidence of PCOS and to study clinical and biochemical characteristics of PCOS among infertility women. Material and Methods: We used the cross-sectional and case control study designs. Total 1334 infertility women enrolled in this study. The study was conducted after approval from the Ethical and research review board of the hospital, and written informed consent was taken from all the women. Among 114 women with PCOS were found by Rotterdam’s criteria at the Infertility and reproductive department, National Center for Maternal and Child Health, between December, 2018 - 2019. Total of 43 females with PCOS were screened among 1334 infertile women. All parameters were assessed either with ELISA in 43 infertile PCOS women and 17 age matched apparently healthy controls diagnosed according to Rotterdam consensus. IDF diagnostic criteria for MS was used. The PCOS patients divided into following groups: (1) with MS ( n=42) and (2) without MS (n=72). Results: The main age, body mass index (BMI), and duration of infertility were 28.7±4.1 years, 27.3±5.2 kg/ m² and 4.4±3.1y, respectively. Among patients 57.9% of them have oligomenorrhea, 22.8% with amenorrhea, primary infertility 57.0% and 51.9% with hirsutism and acne 50.8%. As a result of hormone assays were LH 9.3±3.5mIU/ml, LH/FSH 1.6 ±0.83 [0.1-3.6], AMH 6.1ng/ml ±3.6 /2.9-21.0/. The prevalence of MS was 36.8%. The variables including age (30.9±4.9), body mass (75.9±11.6kg) and also some metabolic parameters which is hypertension (133.6/88.4±13.6 mm Hg), WC (94.1±8.6 cm) and high triglyceride (1.8±1.0 mmol/l) were observed in MS group compared to without MS group. Conclusion Among 1334 women with infertility, the incidence of PCOS 8.7% (116), close to the prevalence in other countries. Considering the diagnose was confirmed of three criteria by the Rotterdam criteria. We found out that the prevalence of metabolic syndrome was 35.3% among infertility women with PCOS. Age, BMI, WC, amenorrhea, acne and acanthosis nigricans, were highly related to metabolic syndrome.