Primary immune thrombocytopenia (ITP) is an acquired autoimmune disease. 1α, 25-dihydroxyvitamin D3 [1,25(OH)2D3] and vitamin D receptor (VDR) play important immune-suppressive roles in immune system. It has been reported that serum 1,25(OH)2D3 were lower in ITP patients. In this study, we evaluated local 1,25(OH)2D3 level and VDR mRNA expression further, and determined whether 1,25(OH)2D3/VDR were correlated with T cell dysfunction in ITP patients. We found that 1,25(OH)2D3/VDR levels were decreased in active ITP patients, and 1,25(OH)2D3 had significant anti-inflammatory effects on ITP patients, including both anti-proliferation of peripheral blood mononuclear cells (PBMCs) and reversing the abnormal T cells polarization. 1,25(OH)2D3 inhibited the differentiation of T helper (Th)1 and Tc1 cells but induced the differentiation of Th2, Tc2 and T regulatory (Treg) cells in ITP patients. However, the percentage of Th17 cells were not affected obviously with 1,25(OH)2D3. In addition, 1,25(OH)2D3 also suppressed pro-inflammatory cytokines (INF-γ and IL-17A) but promoted anti-inflammatory cytokine (IL-10) secretion in ITP patients. In conclusion, decreased 1,25(OH)2D3/VDR might participate in the pathogenesis of ITP, and appropriate supplement of 1,25(OH)2D3 may be a promising treatment.