Background: Clomiphene citrate (CC)-induced ovarian stimulation has been linked to detrimental endometrial consequences that are anti-estrogenic. Objectives: To assess the effects of sildenafil vaginal tablet combined to CC on the endometrial thickness (ET) during ovulation induction. Patients and Methods: This randomized controlled study was conducted at Departments of Obstetrics and Gynecology of Menoufia University Hospital and Alshohadaa Central Hospital. A total of 124 women were recruited. The patients were blinded to group allocation. Group I: (Clomiphene citrate (CC) alone): received clomiphene citrate (50 mg oral tablet twice daily from day 3 to day 7 of the menstrual cycle). Group II: (Clomiphene and sildenafil): received clomiphene citrate (50 mg oral tablet twice daily from day 3 to day 7 of the menstrual cycle) plus vaginal sildenafil tablets (25 mg/12h daily from day 7 up to ovulation trigger). Mean endometrial stripe thickness measured on day 13 of the cycle and pregnancy rates were the primary endpoints. Results: There were no significant differences between both groups regarding demographic, clinical and basal hormonal profiles.The mean ET measured on day 13 of menstrual cycle was statistically significantly higher among patients received clomiphene and sildenafil than those received clomiphene alone (11.09± 3.83 mm versus 9.22± 3.90 mm, p value 0.021). Also, pregnancy rates were 32.3% and 48.4% in group 1 and 2 respectively with significant differences. Conclusion: Incorporation of sildenafil to CC regimen of ovulation induction has a positive impact on endometrial stripe thickness and so pregnancy outcomes.