Abstract: Objective To explore the effect of mifepristone on the proliferation and the expression of nonclassical HLA I molecules (HLA-G and HLA-E) in choriocarcinoma cell line JEG-3. Methods The HLA-G highly positive cell line of choriocarcinoma(JEG-3) was cultured in vitro,and MTT assay was used to examine antiproliferative effect of mifepristone on the JEG-3 cells,the mRNA expression of HLA-G and HLA-E were detected by RT-PCR,and protein level by flow cytometry. Results Mifesitone produced concentration-dependent and time-dependent antiproliferative effect on JEG-3 cell at all experimental concentrations.High-concentration mifesitone could significantly down-regulate both mRNA and protein expression of HLA-G and HLA-E. Conclusion One of mifesitone's antineoplastic mechanisms is surmounting immune tolerance to the neoplasm and inhibit its growth.Key words Mifesitone Human Leucocyte Antigen immune tolerance.