Abstract Background: Sildenafil citrate improves the uterine artery blood flow and the endometrial thickness in women with a prior failed assisted reproductive cycle due to poor endometrial response. Sildenafil citrate can be used orally or by vaginal to improve endometrial receptivity. Aim of Study: To evaluate the efficacy of the orally administered sildenafil citrate on the endometrial thickness and pattern, number of follicles, uterine artery blood flow and pregnancy rate in infertility patients undergoing induction of ovulation. Patients and Methods: The study included one 150 patients who were randomized into two groups: Group A included 75 patients who were given sildenafil citrate 20mg from 8th day to 13th day of the cycle 3 times per day orally and Letrizole 2.5mg from 2nd day till 6th day of the same cycle two times per day orally, and Group B included 75 patients who were given Letrizole 2.5mg from 2nd day to 6th day of the cycle two times per day orally and placebo tablets from cycle day 8 till day 13 three times/day orally. Results: Percentage in change in both RI and PI in both groups founded that it was statistically significant in both groups with p-value <0.001. Biochemical pregnancy rate in both study groups was founded to be higher in group A (Sildenafil Group) than group B (Placebo Group) and was statisticallysignificant between both groups with p-value 0.020. Conclusion: Use of oral sildenafil in endometrial prepa-ration for patient with poor endometrial vascularity showed better endometrial development.