Abstract: Objective To detect the expression of miR-155 and Ets-1 in leukemia cell line K562 and adriamycin resistance K562／A02 cell line， and explore the relationship between miR155， Ets-1 and drug resistance in leukemia treatment. Methods miR-155 simulation oligonucleotide probes and miR-155 inhibitor oligonucleotide probes， Ets-1 expression plasmid and Ets-1 interference expression plasmid were transfected in K562 and K562／A02 cells by Lipofectamine 2000. Real-time quantitative PCR was used to determine the expression of miR-155, Ets-1 and multidrug resistance（MDR1）. The protein levels of Ets-1 and MDR1 were analyzed by Western blotting. The viability of K562 and K562／A02 cells was evaluated by MTT assay. Results The expression levels of miR-155， Ets-1 and MDR1 were significantly increased in K562／A02 cells than those in K562 cells. Down-regulation of miR-155 could obviously increase the inhibition rate of adriamycin on K562／A02 cells and inhibit the expression of Ets-1 and MDR1， which could be reversed by overexpression of Ets-1. While， up-regulation of miR-155 could significantly increase the inhibition rate of adriamycin on K562 cells and stimulate the expression of Ets-1 and MDR1， which could be reversed by Ets-1 siRNA. Conclusion miR-155 is involved in the mechanism of drug resistance in leukemia by regulating Ets-1 expression， which may provide a potential novel target for overcoming drug-resistance.