Abstract: Objective To study the effects of NK cell cytotoxicity against leukemic cell lines KG1a treated with Matrine and to preliminarily explore their molecular mechanisms. Methods The IC50 of KG1a treated with Matrine for 48h was determined with the cck-8 assay and this level of Matrine was chosen to treat KG1a cells.Cytotoxicity of NK cells isolated from 6 healthy volunteers against KG1a cell were analyzed by LDH releasing assay at different effector-to-target cell ratios(E:T) before and after treated with Matrine.The genes expression of NKG2D ligands(MICA,MICB,ULBP1,ULBP2,ULBP3) of KG1a cells by RT-PCR,the expression of NKG2D ligands and HLA-classⅠmolecules were assayed by flow cytometery before and after treated with Matrine. Results The cytotoxicity of NK cells against KG1a cells treated with Matrine was enhanced at 5∶1;10∶1;20∶1 of effect-to-target(P＜0.05).The genes of NKG2D ligands were positively detected in KG1a cells at mRNA level,but there were hardly detected at the protein level.However,the expression of NKG2D ligands of KG1a cells were up-regulated after treated with Matrine(P＜0.05).There was no significant difference of expression HLA-classⅠmolecules between before and after treated with Matrine(P＞0.05). Conclusion The Matrine could obviously up-regulate the NKG2D ligands expression in KG1a cells and thus enhance the cytotoxicity of NK cell against the KG1a cells.