E ndometrial thickness (ET) is one of the best predictors of implantation rate and pregnancy success rate because endometrial growth depends on hormones. Estrogen regulates the proliferative phase, endometrial proliferation induced by estrogen after menstruation is largely dependent on blood flow to the basal endometrium that produces progesterone receptors which are required for progesterone-regulated endometrial growth in the secretory process. To compare the effect of estradiol valerate vs. sildenafil citrate on endometrial receptivity and subsequent pregnancy outcome in unexplained infertility patients receiving letrozole for ovulation induction. Herein, 21 patients with unexplained infertility underwent ovulation induction by letrozole (2.5 mg). Patients were divided into 2 groups; group A (10 patients) were given sildenafil tablets vaginally (25 mg) four times daily and group B (11 patients) were treated with estradiol valerate tablet 2 mg/12 hours. Patients were evaluated by transvaginal ultrasonography (TVS) to determine endometrial thickness, pattern, size, and the number of the dominant follicles, serum assessment of Vascular Endothelial Growth Factor (VEGF) level at trigger day, and chemical pregnancy outcome 14 days later. Results showed that the endometrial thickness, patterns of the endometrium, VEGF, size of the dominant follicle at the trigger day, and pregnancy rates were not significantly different between the two groups. However, the difference in the number of the dominant follicles at trigger day was statistically significant which is more in the sildenafil treated group. The present study confirmed the findings of both Sildenafil and E 2 valerate to boost endometrial receptivity and pregnancy rate.