Background/Aims: To determine the effect of vitamin D<sub>3</sub> supplementation on 25-hydroxyvitamin D [25(OH)D], lipid profile and markers of insulin resistance in obese adolescents. Methods: In this double-blind, randomized, placebo-controlled trial, 58 obese adolescents (n = 58; 12-18 years of age) received either vitamin D<sub>3</sub> (2,000 IU/day) or placebo for 12 weeks. Total 25(OH)D, fasting plasma glucose, insulin and lipid profile were measured at baseline and following supplementation. Results: The trial was completed by 44/58 enrolled participants. At the end of the 12 weeks, total serum 25(OH)D concentrations increased to a modest degree (median 6 ng/ml) in the vitamin D-supplemented group (p < 0.001). Supplementation showed no detectable changes in fasting plasma glucose, insulin, homeostatic model of assessment index (HOMA-IR), lipids and highly sensitive C-reactive protein. Conclusions: 12 weeks of vitamin D<sub>3</sub> supplementation in obese adolescents with 2,000 IU once daily resulted in a modest increase in 25(OH)D concentration in obese adolescents, but did not affect the lipid profile and markers of insulin resistance and inflammation. Further studies with higher doses of vitamin D<sub>3</sub> and/or longer duration of supplementation are needed to understand if vitamin D<sub>3</sub> supplementation can impact lipid profiles and markers of insulin resistance and inflammation in obese children.