Background: Polycystic ovarian syndrome (PCOS) is considered the commonest endocrinological disorder affecting reproductive aged women. PCOS compromises fertility through various pathways. These pathways include hyperandrogenism, insulin resistance and impedance of the uterine and endometrial blood flow. Metformin improves the blood flow to the endometrium. It acts by reducing androgen level and correction of insulin resistance. Endometrial vascular indices were evaluated in this study to evaluate endometrial receptivity in anovulatory patients with PCOS. Aim of the Work: To evaluate the outcome of metformin administration in anovulatory patients with PCOS and its effect on the endometrium. This included its role in ovulation and improvement of pregnancy rates. Patients and Methods: This study included 85 patients from Ain Shams University outpatient infertility clinics from 1 st of January, 2018 till 30 th of June, 2018. We investigated these patients before treatment with ultrasound on day 14, 21. We evaluated endometrial thickness, uterine artery flow pattern, endometrial and subendometrial flow patterns. The patients received metformin 500 mg three times per day for three months. After this duration, we reevaluated them by ultrasound at days 14, 21. Results: Metformin therapy resulted in a significant increase of endometrial thickness and had a significant decrease on uterine, endometrial and subendometrial resistance index (R.I) and pulsatility index (P.I) at day 14, 21 compared to pre-treatment values indicating better blood flow. Conclusion: Metformin therapy resulted in improvement of endometrial flow patterns. Also, it resulted in increase in endometrial thickness and improvement of uterine artery flow.