Introduction: The morbidly weight gain is associated with multiple hormonal interactions with potential negative effect on male fertility. It is not clearly understood if visceral adiposity or Insulin Resistance (IR), or both together, is the key mediator for decreasing the testosterone (T) synthesis and activity in men with metabolic syndrome (MS). The aim: of the study is to establish the influence of IR on the semen levels of Insulin (Ins) and as well as the semen concentration, motility and morphology in men with MS. Material and methods: A pilot prospective study was done among obese men with IR without knowing fertile problems on age between 20-40 years. According to their BMI the participants were divided into three groups: first group (G1), of non-obese subjects with BMI ≥ 19.0 ≤ 24.9 kg/m2, (n1=4); second group (G2) of overweight, pre-obese subjects with BMI ≥ 25.0 ≤ 29.9 kg/m2, (n2=4) and third group (G3) of obese subjects with BMI ≥ 30.0 ≤ 40.0 kg/m2, (n3=21). Semen samples were collected and assayed for Ins, T and standard semen analysis as well. Results: Obesity was associated with significantly increased serum insulin levels and IR, but with no significant difference in serum testosterone level. Significantly severe inverse correlations between serum levels of Ins and T, as well as between BMI and serum T were established. Positive correlation between serum and seminal concentration of Ins was found. A moderately strong negative correlation between concentrations of Ins and T in seminal plasma was confirmed. The significant differences in the average sperm concentration and teratozoospermal index were observed by comparison between obese and non -obese men. Conclusion: This pilot study showed that obesity and IR in general, adversely affects sperm parameters such as decreased sperm motility and increased teratozoospermal index. The pandemic spread of obesity necessitates further studies to clarify the additional links and mechanisms that are manifested at an early stage and are related to violations of reproductive function in obese men.