While psoriasis is not a lethal disease, the disease itself can impact patients' quality of life. Nowadays there are several researches on vitamin D functions. Recently review article of vitamin D deficiency by Holick MF., stated that vitamin D can play a role in decreasing the risk of osteoporosis and other chronic diseases such as malignancy, autoimmune disease, infectious disease, cardiovascular disease, and psoriasis. Moreover, vitamin D effects on keratinocyte by decreasing abnormal cell proliferation, differentiation, apoptosis and controlling immunological process via the suppression of T-cell activation, regulation of cytokine secretion patterns, induction of regulatory T-cell, modulation of T-cell proliferation and interference with T-cell apoptosis.