Objective : This study was performed to investigate the effect of metformin therapy on ovulation induction & pregnancy rate in clomiphene citrate-resistant PCOS women. Method: This study used a randomized, single-blinded, case-controlled methods. Total study group consisted of 21 women who showed clomiphene citrate-resistant parttern on previous ovulation induction cycles. Patients of metformin group received metformin 500 mg three times daily, for 7 weeks. Control group received none. Metformin group was consisted of 10 women and control group was consisted of 11 women. Then clomiphene was administrated at daily 50 mg for 5 days to both groups. Clomiphene dosage was increased to daily 150 mg until ovulation was occurred. Before and After metformin treatment, blood samples for measurement of insulin, glucose, steroids were obtained. Results: In the metformin and control groups, 6 of 10 women (60%) and 2 of 11 women (18%) ovulated. And 4 of 10 women (40%) and 0 of 11 women (0%) conceived. Comparisons between the groups were significant. Conclusion: In PCOS women who are resistant to CC, metformin use increased the ovulation rate and pregnancy rate from CC treatment, significantly.