To investigate the protective effect of epigallocatechin gallate (EGCG) on the immune function of dendritic cells (DCs) after ultraviolet B irradiation (UVB) and its underlying mechanisms, the monocytes were isolated from peripheral blood and cultivated into DCs with cytokines, such as GM-CSF and IL-4. DCs were harvested after cultivation for 7 d and subjected to irradiation with different dosages of UVB. Then, 200 μg/ml of EGCG were added in certain groups immediately after irradiation. DCs simply treated with UVB or treated with both UVB and EGCG were co-cultured with lymphocytes, and MTT assay was used to detect the ability of DCs to stimulate proliferation of lymphocytes. Surface markers CD80, CD86, HLA-DR and CD40 were detected by flow cytometry, and the levels of IL-10and IL-12 secreted from DCs 24 h after cultivation were measured by ELISA. It was demonstrated that UVB irradiation could inhibit the ability of DCs to stimulate the proliferation of lymphocytes and surface expressions of CD80, CD86, HLA-DR and CD40 on DCs in a dose-dependent manner. The inhibition rate of DCs was improved to some extent after treatment with 200 μg/ml of EGCG. When the concentration of EGCG exceeded 100/μg/ml, the enhancing effect of EGCG on the expression of the co-stimulating molecules on DCs could be demonstrated in a dose-dependent manner. UVB showed no significant influence on the secretion of IL-10 and IL-12 from DCs, while EGCG could down-regulate the secretion level of IL-12 and up-regulate that of IL-10. It is concluded that EGCG can antagonize the inhibitory effect on DCs induced by UVB irradiation. This function has some relationship with its protecting effect of the expression of the co-stimulating molecule on the surface of DCs and the secretion level of IL-10and IL-12.