Objective: To evaluate the effect of vitamin D supplementation on ovulation and pregnancy rates in patients with polycystic ovary syndrome (PCOS). Material and Methods: This multicenter randomized controlled clinical trial was performed in the infertility clinics of Tanta University Hospital and Benha University Hospital. One hundred and sixty patients were recruited and allocated into two groups; group 1 served as a control group and group 2 (study group) where patient received vitamin D supplementation. Induction of ovulation with clomiphene citrate. Results: No significant differences were seen in in demographic data: basal hormonal levels, mature follicle size, serum progesterone levels, or pregnancy rate between both groups. Insulin resistance was greater in the control group and resumption of the cycle was higher in the study group. Conclusion: Vitamin D supplementation as an adjuvant to induction of ovulation induction in women with PCOS resulted in enhancement of ovulation and pregnancy rates