Polycystic ovary syndrome represents the most common cause of anovulatory infertility. Deficiency of vitamin D is common, and it's linked to ovarian insufficiency and infertility. The purpose of our study was to determine the effect of supplementation of vitamin D in inducing ovulation in PCOS patients. This prospective controlled clinical study was done in Obstetrics & Gynecology Department in Al-Zahra University Hospital. 50 PCO patients were analyzed in each group. Vitamin D group: included 50 PCOS patients who used 50 mg clomiphene citrate twice daily to induce ovulation starting from the 3^rd day of menstrual period and continue for 5 days added to 10,000 IU of oral vitamin D twice a week and calcium 1250 mg twice daily for 1 month before induction of ovulation and continued for 3 induction cycles. Control Group: included 50 PCOS patients who used 50 mg clomiphene citrate twice daily to induce ovulation starting from the third day of menstrual cycle and for 5 days added to a placebo tablet which given twice a week and calcium 1250 mg twice daily for period of 1 month prior to ovulation induction and continued for 3 induction cycles. Vitamin D supplementation showed significant benefits according to ovulation after adding to clomiphene citrate during ovulation induction among PCOS patients.