Previous studies in overweight men have shown an increased likelihood of abnormal semen parameters. Obesity has been found to be associated with male subfertility. In this study we aimed to investigate the effect of obesity on semen parameters and hormone levels in infertile males. This was a prospective crosssectional study designed to assess the influence of obesity on semen parameters and hormone levels in infertile men. 88 obese [Body mass index (BMI) ≥30 kg/m2] men and 169 non-obese (BMI<30 kg/m2) men were eligible for the study. All semen samples were obtained by masturbation after 3 days of sexual abstinence. After liquefaction at room temperature, semen volume, sperm concentration, motility, and normal morphology were determined according to World Health Organization (WHO, 2010) guidelines for semen analysis. Serum hormone levels were measured on the same-day with semen analysis. Semen volume was significantly lower in the obese group than in the non-obese group. No significant differences were observed between the groups in term of other semen parameters. Mean serum total testosterone (TT) level and TT/estradiol (E2) ratio were significantly higher in the non-obese group, whereas mean E2 level was significantly higher in the obese group. There was a significant positive correlation between BMI and E2 levels in the obese group. A significant inverse correlation was observed between BMI and TT levels in the non-obese group. Obesity may reduce semen volume in infertile males. This effect may be due to the changes in sex hormone levels. However, it has no impact on more meaningful indicators of male fertility such as sperm concentration, motility, and morphology.