Aim [WT5”BZ]To investigate the mechanism involved in the apoptosis of human myeloid leukemia U937 cells induced by oxidized low density lipoprotein (ox-LDL).[WT5”HZ] Methods[WT5”BZ] The apoptotic cells were determined by flow cytometry and DNA fragmentation assay. The content of p53, p21 and Bcl-2 protein were analyzed by immunofluoresence staining and flow cytometric analysis. The level of p53,p21 and Bcl-2 mRNA were quantified by reverse transcription-polymerase chain reaction (RT-PCR). [WT5”HZ]Results [WT5”BZ]Ox-LDL induced apoptosis of U937,which is concentration dependent,and upregulate the level of p53 and p21 mRNA and protein as detected by RT-PCR and flow cytometric analysis.However,expression of Bcl-2 was downregulated after treatment with ox-LDL. [WT5”HZ]Conclusion [WT5”BZ]Ox-LDL upregulated the gene expression of p53, p21 and downregulated Bcl-2 expression, which induced apoptosis of U937 cells.