Introduction: Obesity is a major public health problem. Its impact on male infertility is controversial. We aimed to explore the relationship between increasing male body mass index (BMI) and the change in semen parameters and recognize the ones most affected. Objectives: Explore the relationship between the male BMI and their semen parameters & recognize the most affected parameter. Materials and methods: It is a prospective study involving 221 men who were distributed into groups according to the BMI (kg/m²)—underweight (<18.5), normal (18.5–22.9), overweight (23.0–24.9), and obese I (25–29.9) obese II (>30). Their semen analysis was done as a part of the routine evaluation, and that was correlated with the BMI. The statistical significance was determined using the p-value, obtained by analysis of variance (ANOVA) testing. p-value <0.05 was considered statistically significant. Results: The pairs: normal vs obese I, normal vs obese II, and overweight vs obese I have statistically significant mean differences for the volume. The pairs: normal vs obese I and normal vs obese II have statistically significant mean differences for progressive motility. The pairs: normal vs obese I have a statistically significant mean difference for total motility while using a family error rate of 0.05. Conclusion: Obese men had significantly reduced semen volume, progressive, and total motility. The sperm concentration and morphology also showed abnormal values with increasing BMI, but the relationship was not statistically significant. Oligospermia in the underweight group was incidentally noted. We concurred that maintaining a normal BMI augments a man’s fertility potential.