Background: the polycystic ovary syndrome (PCOS) is important cause of an ovulatory infertility and a notable proportion of women of reproductive age are affected. Different factors could result in different manifestations and many of these are related to predispositions. Objectives: The study was carried out to study the improvement of ovulation induction in obese patients with Polycyctic ovarian syndrome (PCOS). Subjects and methods: This is prospective clinical trial that was conducted in the infertility unit of Zagazig university Hospital on 120 patient suffering from PCOS were included in this study during the period from Actober 2018 to May 2019. This trial was designed to compare the improving induction of ovulation in obese females with Polycystic ovarian syndrome undergoing induction of ovulation by Clomid and Metformin (n=60) or Letrozole (n=60).Results: There was no significant statistical difference between Clomid and Metformin group and letrozole group in term of pregnancy rate, There was a significant statistical difference between Clomid and Metformin group and letrozole group in term of Size of dominant Graafian follicle (on day 11) (p=0.03) and the Size of dominant Graafian follicle (on day 13-14) (p=0.01).Conclusion Letrozole improves endometrial thickness and cervical mucosa and causes monofollicular ovulation but action of clomiphene citrate combined with metformin improved the ovulation and increased total number of follicles. Therefore, Letrozole can be used for the ovulation induction improvement in obese women having PCO