Asthma is a prolonged respiratory disease related with hyper-responsiveness and increased inflammation of airways; affects millions peoples worldwide. Vitamin D possess anti-inflammatory and immunomodulatory activities (1). Its deficiency (the level less than 20 ng/mL in the serum) is found to be related to occurrence of pulmonary diseases including bacterial and viral infections and asthma. Some studies indicate that low levels of vitamin D in the serum are related to reduced lung function and increased airway inflammation as well as overall poor results in asthmatic patients. Thus, it provides positive relation between vitamin D and asthma. This article discusses how the results of clinical trials are inconsistent and do not provide supportive information about positive role of vitamin D in asthma. The results of the authors showed that little or even no effect of supplementation of vitamin D in improvement of onset, symptoms or progression of asthma was found in comprehensive interventional studies in adults, children and pregnant woman, and that's what the authors conclude.