Background: Due to inconsistent evidence regarding the potential role of vitamin D on lipid profile and sirtuin 1 (SIRT-1), this study was designed to investigate the effect of vitamin D supplementation in combination with weight loss diet on lipid profile and SIRT-1 in obese subjects with vitamin D deficiency. Methods: Forty-four obese subjects with vitamin D deficiency were randomly assigned in a randomized clinical trial to receive either a weight reduction diet supplemented with 50 000 IU vitamin D3 pearl (n = 22) or placebo (n = 22) once weekly for 12 weeks. Changes in total cholesterol (TC), low-density lipoprotein cholesterol (LDL-C), triglyceride (TG) and low highdensity lipoprotein cholesterol (HDL-C) and SIRT-1 were the primary outcomes. Secondary outcomes were changes in body mass index (BMI), 25(OH) D and parathyroid hormone (PTH). Physical activity and dietary intakes were also assessed. Results: During the intervention, PTH (mean difference,-33. 36; 95% CI:-49. 15 to-17. 57; P < 0. 001) and LDL-C (mean difference,-15. 91; 95% CI:-21. 76 to-10. 07; P < 0. 001) decreased and 25(OH) D (mean difference, 36. 44; 95% CI: 29. 05 to 43. 83; P < 0. 001) increased significantly in the vitamin D group. BMI (mean differences:-2. 40; 95% CI: [-2. 92 to-1. 88] in vitamin D group and mean differences:-1. 90; 95% CI [-6. 58 to-3. 01] in placebo group, P < 0. 05 for both groups), TC (mean difference,-21. 31; 95% CI:-27. 24 to-15. 38; P < 0. 001 in vitamin D group and mean difference,-12. 54; 95% CI:-19. 02 to-6. 06; P < 0. 001 in placebo group) and TG (mean difference,-21. 31; 95% CI:-27. 24 to-15. 38; P < 0. 001in vitamin D group and mean difference,-12. 54; 95% CI:-19. 02 to-6. 06; P < 0. 001 in placebo group) decreased and SIRT-1 (mean difference, 3. 95; 95% CI: 1. 18 to 6. 73; P = 0. 007in vitamin D group and mean difference, 1. 91; 95% CI: 0. 31 to 3. 63 in placebo group, P = 0. 022) increase significantly in both group. At end of the study, 25(OH) D and PTH showed significant differences in between-group analyses (P < 0. 05). No significant difference was detected for HDL-C in within and between groups. Conclusion: This study gives no support for any beneficial effect of vitamin D supplementation on lipid profile and SIRT-1 in obese subjects with vitamin D deficiency.