Reduced serum magnesium (Mg) levels have been associated with obesity, insulin resistance (IR), type 2 diabetes, and metabolic syndrome in adults. However, in the children population, the evidence is still limited. In this cross-sectional study, we aimed to analyze the association of serum Mg levels with the frequency of overweight and obesity and cardiometabolic traits in 189 schoolchildren (91 girls and 98 boys) between 6 and 12 years old from Mexico City.Anthropometrical data were collected and biochemical parameters were measured by enzymatic colorimetric assay. Serum Mg level was analyzed by inductively coupled plasma mass spectrometry (ICP-MS). The triglyceride-glucose (TyG) index was used as a surrogate marker to evaluate IR.Serum Mg level was negatively associated with overweight (Odds ratio [OR] = 0.377, 95% confidence interval [CI] 0.231-0.614, p