Abstract: 　Objective　To explore the effects of 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) on the stimulating ability of cord blood monocytes-derived dendritic cells (DCs) to T cells proliferation. Methods　Umbilical cord blood was collected in aseptic condition. Cord blood monocytes were isolated and cultured for 8 days in the presence of rhGM-CSF, rhIL-4 and rhTNF-α for inducing to differentiate DCs, then intervened by 1,25(OH)2D3 (10 nmol/L). The expressions of differentiation and maturation markers on dendritic cells were determined by flow cytometry. Mixed lymphocyte reaction (MLR) was used and T cells were stained with CFSE to observe the stimulating ability of DCs to T cells proliferation by flow cytometry. Cytokines in the culture medium of MLR were measured by ELISA. Results　1,25(OH)2D3 treated-DCs stimulated less CD3+ T cells to proliferate than control group (61.6±8.23 vs. 75.21±6.21, P<0.01). Moreover, lower proliferation of both CD3+CD4+ and CD3+CD8+ T cells was observed in intervention group (59.24±10.22 vs. 74.54±6.89, P<0.05; 47.06±12.10 vs 59.97±9.11, P<0.05) . The IL-12 and IFN-γ levels in the culture medium of MLR in intervention group were significantly lower than control group (78.84±11.8 vs .99.06±9.07, P<0.05; 9.76±2.75 vs. 22.45±2.6, P<0.05), however, the IL-4 level in intervention group were significantly higher than control group (49.45±2.84 vs. 35.75±1.89, P<0.01). Conclusions　1,25(OH)2D3 inhibits the capability of DCs to activate CD3+CD4+ and CD3+CD8+ T cells, and instructs DCs to induce Th2 bias.