To investigate the relationship between nm23-H1 gene and human chronic myeloblastic leukemia we designed siRNAs which target nm23-H1 gene. According to the principles of designing siRNA, we selected three siRNAs and transfected them into K562 cells by lipofectamine2000. The expression levels of nm23-H1 mRNA were detected by reverse transcriptase polymerase chain reaction after transfection for 24 hours. The expression levels of nm23-H1 protein were assayed by immunocytochemical method after transfection for 48 hours. And after transfection for 24, 48 and 72 hours, cell proliferation was determined by MTT method. Among the three siRNAs, siNM526 can effectively inhibit the expression of nm23-H1 on mRNA and protein levels. The growth of K562 cells was suppressed after transfection of siNM526. These results suggest that low expression level of nm23-H1 in K562 cells inhibited cell proliferation, namely reduced malignant degree of them. Therefore nm23-H1 gene might be a potential target of leukemia treatment.