Vitamin D is a fat-soluble vitamin, which is obtained by conversion of 7-dehydrocholesterol in the skin by UV ray and by diet. Its role on bone mineralization has been known for over two hundred years, while its non-skeletal effects have been acknowledged only in the last few years. The discovery of important vitamin D properties on the innate and adaptive immune system created a lot of interest in a potential role of vitamin D on diseases characterized by heightened inflammation and oxidative response, and impaired antimicrobial response, such as asthma and chronic obstructive pulmonary disease (COPD). Recent studies have demonstrated that vitamin D and its deficiency have a number of biological effects which are potentially important in altering the pathogenesis and severity of both asthma and COPD. Vitamin D may improve lung function and response to steroids therapy, reduce airway remodeling and disease exacerbations. The aim of this study is to review the role of Vitamin D in asthma and COPD.