Background and study aim: Epidemiological and experimental data correlated hypovitaminosis D to the pathogenesis of NAFLD. So, the aim of this study was to evaluate the role of vitamin D in NAFLD patients with hypovitaminosis D. Patients and Methods: We studied 78 consecutive patients with biopsy-proven NAFLD. Patients were divided into 2 groups according to serum level of 25 (OH) D; group I; have deficient 25 (OH) vitamin D (<50nmo/L) and group II; have sufficient 25 (OH) vitamin D (50-70 nmol/L). Liver injury profile (ALT, AST), lipid profile (LDL, HDL and triglycerides), inflammatory marker (CRP) as well as histopathological assessment according to NAS scoring were evaluated at baseline. Vitamin D supplementation for 24 weeks was given for both populations with follow up evaluation of laboratory parameters at the end of the study. Results: Patients with deficient 25 (OH) vitamin D levels had significantly more severe NAFLD than those with sufficient 25 (OH) vitamin D levels at baseline. After 24 weeks of high dose vitamin D supplementation there was significant improvement in lipid profile (LDL, HDL, and triglycerides), hepatic transaminases (ALT, AST) and CRP in NAFLD patients with hypovitaminosis D, but no significant changes in NAFLD patients with sufficient vitamin D. Conclusion: Correction of hypovitaminosis D may have beneficial effects on NAFLD in patients with moderate to severe activity but no effects in case of sufficient vitamin D.