Abstract 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 deter-mine 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 & im-proved 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.