Background: Polycystic ovary syndrome (PCOS) is one of the most common endocrine disorders diagnosed in women. The prevalence of polycystic ovary syndrome is estimated to be between 2.2% and 26% among women. Inflammation is thought to play a role in the pathogenesis of PCOS. Quercetin is a flavonoid that has been shown to be anti-inflammatory and antioxidant so, the aim of this study was to differentiate between the effects of two doses of quercetin & to provide natural, safe, and effective treatment of polycystic ovary syndrome. Aim of Study:The aim of the present study was to determine the role of quercetin in treatment of Letrozole Induced polycystic ovary syndrome in rat model and determine the effects of two different doses of quercetin.Material and Methods: Adult nonobese female rats were induced to polycystic ovary syndrome by using 1mg/kg of letrozole and confirmed to be diseased by vaginal smears. A group of the experimental rats received 50mg/kg of quercetin; another group received 100mg/kg of quercetin & another one received 100mg/kg of metformin. LH, FSH, (LH/FSH) ratio, hormonal profile, catalase, TNF-a , serum glucose level, insulin sensitivity and ovarian morphology by hematoxylin & eosin (H&E), Masson trichrome (MTC), periodic acid-Schiff (PAS) & anti transforming growth factor beta (TGF-P) stains were then assessed in addition to the weight of the rats and their temperature after induction and after treatment. Results: Treatment with quercetin significantly decreased testosterone & TNF-a and increased FSH, LH, estrogen, progesterone & catalase. It decreased body weight & body hair distribution. It also improved insulin sensitivity & improved histological structure of the ovary. 100mg/kg of quercetin had better results than the dose of 50mg/kg of quercetin & metformin in the parameters we measured. 50mg/kg of quercetin & metformin were comparable in their results.