Although some data exist on use of insulin sensitizers (eg, metformin, thiazolidinediones) in women with CC–resistant PCOS, at present, the consensus for infertility treatment related to PCOS is that there is no advantage to adding these agents to accepted fertility drugs. For these reasons, other therapies are needed for a subset of women with PCOS and infertility. The present study was designed to compare the efficacy of combined aromatize inhibitors Letrozole with metformin versus CC with metformin in CC Resistant PCOS. This study was done on sixty documented CC Resistant PCOS. All of them received metformin for six weeks, then they were divided to two groups, both of them continued on metformin. The 1st group received two tablets of CC 50mg/day from the 3rd day for five days and the 2nd group received two tablets of aromatase inhibitor Letrozole 2.5 mg/day from the 3rd day for five days. These cases will were followed up for three cycles by transvaginal ultrasound folliculometry and serum progesterone on day 21 of the cycle to document ovulation. The results of the present study revealed both lines of treatment were effective in treatment of CC-resistant PCOS patients, no statistically significant difference was found between CC group and letrozole group as regard ovulation rate, number of follicles in the end of first, second or third cycles, or as regard the diameter of follicles, i.e., both regimens showed efficacy to the same extent.