Background: Egyptian infertile obese women with polycystic ovary syndrome (PCOS) were markedly increased in ART Unit for infertility treatment undergoing ICSI. In a trial to enhance the ovulation, fertilization response and pregnancy outcome treated patients with Metformin as insulin sensitizing drug, 3 months before ICSI processing. The aim of this study was to evaluate the effect of Metformin on the hormonal profile, lipid and lipoprotein profile and insulin resistance in obese PCOS patients undergoing ICSI. Setting: This study was conducted at International Islamic Center for Population Studies and Research, Assisted Reproduction Unit, Al-Azhar University during the period between 2009 and 2011. Design: A prospective randomized study. Patient and Methods: A total of 75 patients with obese PCOS were randomized to receive oral Metformin for three months. For each patient, FBS and Hb, hormonal profile included FSH, LH, FSH/LH ratio, E 2 and PRL, lipid and lipoprotein profile included total cholesterol, LDL, HDL and triglycerides evaluation were performed at baseline and after 3 months of treatment. Results: There was a significant decrease in the FBS in cases treated with Metformin when compared with control or obese PCOS, no significant differences were noticed in the level of Hb% in both groups. Total lipids, triglycerides and total cholesterol were decreased significantly compared with obese PCOS group. Significant decrease was also observed in respect to LDL in cases of Metformin than cases of obese PCOS. Significant increase in the level of HDL was recorded. Significant decrease was detected in FSH, LH and FSH/LH ratio in Metformin treated group while no difference was observed in prolactin or estradiol hormonal profiles. Observed improvement was detected in the number of received HMG ampoules, mature oocytes, number of grade A embryos and in pregnancy outcome. Conclusion: Metformin as lowering insulin resistance, improving the response in obese PCOS women undergoing ICSI, by enhance their resistance sensitivity in transadipose tissue leads to improvement the function of gonads and hormonal and lipids profile .This improvement was detected by decreased total cost for ICSI, lowering the number of both given stimulation ampoules and mature collected oocytes and finally the percent of successful pregnancy rate. [ABSTRACT FROM AUTHOR]