Objective: Although various studies have linked environmental toxins, mumps infections, alcohol consumption, and abnormal body mass index (BMI) to impaired semen quality, the precise causes of infertility remain unclear. This study investigates the impact of BMI on oxidative stress markers in semen analysis among infertile men, illuminating the role of oxidative stress in cases of unexplained infertility. Methods: In this cross-sectional study, 280 patients exhibiting infertility symptoms were recruited. Comprehensive semen analysis was conducted, evaluating reactive oxygen species (ROS) levels, sperm plasma membrane lipid peroxidation via flow cytometry, total antioxidant capacity (TAC), and results from the sperm chromatin structure assay. Participants were categorized based on their BMI, facilitating comparisons between obese and non-obese individuals. Results: Both BMI and age significantly influenced male fertility, particularly in obese individuals. Strong correlations were identified between elevated BMI, increased ROS levels, and decreased TAC. The obese infertile group exhibited substantially lower TAC compared to controls, highlighting obesity's detrimental effect on antioxidant defenses. Furthermore, significant reductions in sperm count, motility, and normal morphology were observed, alongside an increase in non-motile sperm. These outcomes demonstrate the complex relationship among oxidative stress, BMI, and fertility, emphasizing the necessity for targeted interventions addressing obesity's effects on reproductive health. Conclusion This study underscores the importance of managing obesity and understanding its impact on oxidative stress as essential components in improving reproductive outcomes among affected men.