Background: The prevalence of childhood obesity has significantly increased in Korea. This study aimed to use data from the 2010 Korea National Health and Nutrition Examination Survey (KNHANES) to investigate the association between sodium (Na) intake and insulin resistance in children and adolescents with obesity. Methods: The study population consisted of 578 adolescents aged 12–18 years who were enrolled in the 2010 KNHANES. Subjects were classified into the following four groups based on their body mass index (BMI) and homeostatic model assessment-insulin resistance (HOMA-IR) values: normal BMI and HOMA-IR (Group 1), normal BMI and ≥75% HOMA-IR (Group 2), ≥85% BMI and normal HOMA-IR (Group 3) and ≥85% BMI and ≥75% HOMA-IR (Group 4). The groups were further divided into four quartiles (Q1–Q4) based on urinary sodium-creatinine ratios (UNa/Cr) to analyze the association between obesity and metabolic abnormality as a result of increased Na intake. Results: There were significant differences among the four groups in terms of abdominal obesity (p<0.000), waist circumference (WC) (p<0.000) blood glucose levels (p<0.000), insulin levels (p<0.000) and UNa/Cr, with Groups 2, 3 and 4 having significantly higher UNa/Cr than Group 1 (p=0.002). In addition, there was a significant positive correlation between UNa/Cr and obesity (Q1=1 vs. Q4=3.23, p=0.019) and metabolic abnormality (Q1=1 vs. Q4=2.25, p=0.167). Conclusions: Increased Na intake showed a positive statistical correlation with insulin resistance and is associated with an increased risk of insulin resistance and other metabolic abnormalities in obese children and adolescents.