The present study was designed to evaluate the relationship between serum leptin and infertility in obese young and old men and women. The groups of infertile obese men (n=66) and women (n=30) compared with control obese fertile men (n=60) and women (n=30) with same ages to find the contribution of serum leptin level in causation of fertility. The results revealed that serum leptin were significantly raised in infertile male and female with p<0.001. BMI was also found to be significantly higher (p<0.001) in infertile men and women. Moreover a strong positive correlation was found between BMI and leptin level, and serum leptin and age in both fertile and infertile men and women. The values of correlation coefficients between serum leptin and BMI, and serum leptin and age are statistically significant (r=0.3-0.6, p<0.01-p<0.05). This study has concluded that obesity is associated with infertility in men and women. Sex hormonal imbalance may also be associated BMI and serum leptin in infertility. However further studies are required to determine the exact match by which enhanced BMI and serum leptin levels to female and male infertility.