Background: Leptin, a key hormone in energy homeostasis and neuroendocrine function, has a permissive role in the pathogenesis of reproductive dysfunction. Objective: To assess the role of serum leptin in women with PCOS and to evaluate leptin and insulin levels in PCOS women before and after treatment with metformin. Materials and Methods: Sixty women of reproductive age (18- 38years) were allocated to four groups: 15 obese women with PCOS (BMI >30 kg/m2), 15 obese controls, 15 non-obese women with PCOS (BMI 18 -30 kg/m2), and 15 non-obese controls. Serum leptin and insulin levels were measured and compared between case and control subjects also comparison done pretreatment and after treatment with metformin. Results: There was a significant increase in leptin in nonobese PCOS compared to non-obese control (5.64±1.43), (P value=0.0032), insulin level was significantly higher in PCOS group (15.87±6.65) than control (5.47±1.68), (P value<0.001). There was significant decrease in BMI, leptin and insulin levels after 12 month of metformin treatment in obese and non-obese PCOS subjects. Conclusion: Leptin level increased remarkably with increasing body weight and it is higher in non-obese PCOS women in comparison with non-obese healthy women.