Background: Endometrial thickness is a marker of endometrial receptivity and a prognostic factor for embryo transfers (ET). Poor endometrium is a multifactorial condition; so, its management should be cause-related. One of the treatment options is Sildenafil citrate intake. It causes uterine vascularity improvement. Objectives: The aim of the current work was to evaluate the effects of vaginally administered doses of sildenafil on endometrial lining and ICSI outcome in infertile women with poor endometrial development. Patients and Methods: This study included a total of thirty infertile women with at least one prior ICSI failure attributed to inadequate endometrial development, undergoing ICSI procedure attending at a private assisted reproductive center. All patients underwent ICSI using a long GnRH-a protocol with the addition of sildenafil vaginal suppositories (20 mg, 4 times per day) for 10 days beginning with ovulation induction and continued until trigger day. Results: The results showed that increased endometrial thickness due to treatment with sildenafil to reach 12-14 mm in 28 out of 30 cases and was associated with a pregnancy rate of 60.7% if compared to the same group thickness. Also, another effect of sildenafil citrate was increasing the endometrial trilaminar pattern in 27 case and subsequently with high pregnancy rate. Conclusion: Increased endometrial thickness due to sildenafil therapy was associated with high pregnancy rat and its intake was associated with increased trilaminar endometrial pattern in 90% of patients which causes high pregnancy rate.