Abstract: OBJECTIVE To investigate the effects of xanthatin on allergic dermatitis and its mechanism. METHODS Fluorescein isothiocyanate (FITC)-induced Th2 allergic contact dermatitis (ACD) was used and the effects of xanthatin on ear swelling， ear histopathology， spleen index and Th2 cytokines IL-4， IL-5 and IL-13 in mice ear homogenate were observed. The proliferation of xanthatin on HaCaT and RAW264.7 cells， and spleen lymphocytes were investigated by MTT assay. ELISA was used to detect the expression of thymic stromal lymphopoietin (TSLP) in epithelial cells induced by poly(I∶C) and TNF-α， and TNF-α in RAW264.7 induced by LPS. RESULTS 40 mg/kg xanthatin significantly inhibited ear swelling and reduced the production of Th2 cytokines IL-4 and IL-5 in ear homogenates in ACD mice. Ear pathology showed that xanthatin could improve the infiltration of inflammatory cells. In vitro， xanthatin obviously inhibited the production of TSLP in epithelial cells. Also， it markedly inhibited the production of TNF-α in RAW264.7 cells. While there was no significant effect on the activation of T lymphocytes and B lymphocytes induced by concanavalin A (ConA) and LPS. CONCLUSION Xanthatin shows obvious therapeutic effects on allergic dermatitis， and it may play an anti-inflammatory effect through inhibiting TSLP produced by epithelial cells and TNF-α produced by macrophages.