As the number of obese patients increases, childhood obesity also increases and it is recognized as a big problem because it increases the incidence of hypertension, hyperlipidemia, diabetes and metabolic syndrome. Although thyroid hormone abnormalities sometimes exist in obese patients without thyroid disease, there is still much controversy on the impact of obesity on thyroid hormone test results. Accordingly, the present study investigated the correlation between obesity and thyroid hormone concentrations in children with normal thyroid function. In the present study, 356 patients aged 6-18 years who visited the Chosun University Hospital were randomly selected, after exclusion of those with thyroid disease, diabetes mellitus, kidney disease, those with a history of smoking and drinking, and those taking steroids or lipid lowering agents. There were no significant differences in levels of thyroid stimulation hormone (TSH) and free thyroxin (fT4) between males and females. The patients were divided into groups based on serum TSH concentration: group A with TSH < 4.0 μIU/mL and group B with TSH ≥ 4.0 μIU/mL (upper level of normal range). BMI z score, ALT, rGTP, and total cholesterol were significantly higher in group B. Multiple regression analysis adjusted for age, gender, birth weight, and pubertal development showed that TSH and BMI z score were positively correlated, while fT4 was not correlated with other factors.