Background: Patients who had thinner endometrium could be managed using sildenafil citrate, which could be efficient in enhancing endometrial development pregnancy outcomes; clomiphene citrate is first-line treatment for anovulation. The present study aimed for evaluation of effectiveness adding sildenafil citrate to clomiphene citrate as adjunct treatment line for ovulation induction. Subjects and methods: We carried out this randomized controlled clinical trial on 98 cases with primary infertility, 49 cases in every group. From 3rd to 7th day seven, participants in groups A and B took 50 mg CC (Clomid) orally twice daily to induce ovulation. From Day eight until ovulation was triggered, members of group B also received 25 mg of Sildenafil orally once every 12 hours. frequency of pregnancies in two groups was subsequently evaluated. Results: This study revealed a significantly higher follicular size on day 9 in group A (15.56 ± 2.39) vs (13.42 ± 2.25) in group B. A statistically significant difference was revealed in thickness of endometrium between two studied groups in < 7mm and 7 -13mm (p=0.005, 0.013, respectively); in group B (clomiphene with sildenafil), 41 patients (83.7%) had endometrium of 7 to 13 mm. We found that pregnancy rates in group B were 25 cases (51%); 23 patients got pregnant with endometrium thickness from 7-13mm, while only two patients got pregnant with endometrium thickness >13mm, no pregnancy recorded endometrial thickness less than 7mm. Conclusion: Sildenafil citrate could increase pregnancy rates among women who are undergoing ovulation induction using clomiphene citrate by increasing endometrial thickness