Abstract: Objective :To study the effect of dexamethasone on the protein and mRNA expression of RANTES in asthmatic mice. Methods: Thirty female BALB/c mice were randomly divided into three groups(10 mice in each group) : control group\asthmatic group \dexamethasone group . Bronchoalveolar lavage fliud (BALF) were collected for counting cells and the percentage of eosinophils (EOS); RANTES concentrations in BALF and serum were measured by ELISA.The pathologic changes of bronchi and the left lung tissue were evaluated and stained with hematoxylin and eosin(HE), Immunohistochemistry was used to measure the level of RANTES protein in the lung tissues of asthmatic mice.In situ hybridization was used to measure the level of RANTES mRNA in the lung tissues of asthmatic mice.Results :The total cells、percentage of EOS、concentrations of RANTES in BALF and serum in asthmatic group was significantly different from control group (P<0.01); Dexamethasone group were significantly different from asthmatic group (P<0.01). The expressions of RANTES protein and RANTES mRNA around the lung tissue of asthmatic group were significantly elevated than those of control group (P<0.01), the epithelial cell was the chief expression cell, the expressions of RANTES protein and RANTES mRNA around the lung tissue of dexamethasone group were significantly lower than those of asthmatic group (P <0.01).Conclusion: Dexamethasone demonstrates anti-inflammatory effects partly by downregulating the expressions of RANTES protein and RANTES mRNA.