Background: Vitiligo is an acquired, progressive, multifactorial, depigmenting disorder characterized by the appearance of circumscribed white macules in the skin due to chronic progressive loss of functional melanocytes in the epidermis. The etiology of vitiligo is not clear, although various hypotheses have been proposed. Objective: To evaluate the serum levels and the possible role of 25 OH vit D in vitiligo and to detect whether its level is modulated by Narrowband ultraviolet (B NB-UVB) therapy. Patients and Methods: The current study included 30 patients with vitiligo. In addition, 30 healthy subjects who were age and gender matched, served as a control group. All persons were recruited from the outpatient clinic of Al-Azhar University hospital (Damitta) and from Dermatology, Leprosy and Venereology Mansoura Hospital, from March 2018 to June 2018. Results: Vitamin D levels were lower in patients with vitiligo as compared to the control subjects. Levels of vitamin D increased significantly after NB-UVB therapy. Also, VASI scores showed improvement after NB-UVB therapy. The mean VASI score in both groups showed highly significant decrease after treatment by NB-UVB. Comparison and correlation between VASI before NB- UVB therapy and 25(OH) D showed good negative correlation. Conclusion: Decreased vitamin D serum level was found in vitiligo patients, indicating its possible involvement in the pathogenesis of the disease. This level was increased significantly after NB-UVB therapy. In addition, vitamin D serum level correlated negatively with the severity of the disease.