Abstract: Abstract：【Objective】To observe the changes of the probability of inhibition and the mitogen-activated protein kinase phosphatase-1(MKP-1)expression in human breast adenocarcinomal cell after dexamethasone pretreatment with difficult concentration and treatment of paclitaxel. 【Methods】MTT assay (mononuclear cell direct cytoxicity assay) : to estimate the survival rate of paclitaxel on breast adenocarcinomal cell MCF-7 , screening the concentration of IC50 in this medicine. To place different concentration of dexamethasone pretreatmently and paclitaxelsuccedently on MCF-7 cell，MTT assay to estimate the survival rate of paclitaxel on MCF-7 cell and reverse transcriptase-polymerase chain reaction(RT-PCR)to detect the expression level of the mitogen—activated protein kinase phosphatase-1 （MKP-1）mRNA in MCF-7 cell( P < 0.05). 【Results】After being pretreatmented with dexamethasone with difficult concentration，MCF-7 cell was induced inhibition of chemotherapy to paclitaxel，the inhibition rate increased gradually with the increasing concentration of dexamethasone and the expression level of MKP-1 mRNA increased gradually with the increasing concentration of dexamethasone also. 【Conclusions】After being pretreatmented with dexamethasone with difficult concentration，MCF-7 cell was induced inhibition of chemotherapy to paclitaxel，which make clear that MKP-1 may be involved in the path-ways of chemotherapy inhibition to breast carcinomas through resistance cellular apoptosis.

Key words: Glucocorticoid, Breast adenocarcinomal cell strain, Paclitaxel, Inhibition, MKP-1