Study Model/Methodology: This is a cross-sectional study with a sample of 104 overweight/obese adolescents, with a mean weight of 52.98 kg ± 22.00, mean age 16.01 ± 2.91 years. We used the homeostasis model assessment-estimated IR (HOMA-IR) index to quantify the insulin resistance (IR). The -308 polymorphism of the promoter of TNF-α was performed using polymerase chain reactionrestriction fragment length polymorphism technique. Statistical analysis of the quantitative measures was conducted with a student’s t-test. For correlation between the genotype and alleles, we used chisquare statistical test. To test the heterogeneity between HOMA-IR and the anthropometric parameters the Mann-Whitney test was used, associated with the Hardy-Weinberg equilibrium. The association between -308G/A polymorphism of the promoter of TNF-α and HOMA-IR was tested by univariate linear regression analysis. Objective: Investigate the association between -308G/A polymorphism in the promoter of tumor necrosis factor-alpha (TNF-α) and susceptibility to IR in overweight/obese adolescents. Results: The prevalence of IR was 18.30% according to the HOMA-IR. The frequency of GG, AG and AA genotype was found 75 (72.12%), 28 (26.92%) and 1.0 (0.96%) respectively. Allele frequencies for guanine (G) and adenine (A) were 178 (85.58%) and 30 (14.42%), respectively. The allele A as well as GA and AA genotype contributed to increase RI (14.42% and 27.88% respectively). Conclusion: The - 308 G/A polymorphism of the promoter of TNF-α can contribute to the IR increase in obese adolescents with GA and AA genotypes.