[ ABSTRACT] AIM: To investigate the protective effect of autophagy on oxidized low density lipoprotein ( ox-LDL)-induced macrophage apoptosis and the underlying molecular mechanisms .METHODS:The RAW264.7 macropha-ges were pretreated with 3 mmol/L 3-methyladenine (3-MA), 1 μmol/L rapamycin (Rap) or 4 mmol/L 4-phenylbutyric acid ( PBA) respectively for 1 h and then treated with ox-LDL (100 mg/L) for 12 h.The cell viability and apoptosis were determined by MTT assay and flow cytometry with Annexin V-FITC/PI staining, respectively.The activities of lactate de-hydrogenase ( LDH) in the medium and caspase-3 in the cells were determined by detection kits .The protein levels of bec-lin-1 (a molecular marker of autophagy ), glucose-regulated protein 78 (GRP78, an endoplasmic reticulum stress marker) and C/EBP homologous protein ( CHOP, a key-signaling component of endoplasmic reticulum stress-induced apoptosis ) were examined by Western blot .Microtubule-associated protein 1 light chain 3 (LC3, another molecular marker of autoph-agy) was observed under laser scanning confocal microscope .RESULTS: Treatment of the RAW264.7 macrophages with ox-LDL at 100 mg/L for 12 h resulted in significant decrease in cell viability , and dramatic elevation in LDH leakage , cell apoptosis and caspase-3 activity, which were promoted by 3-MA (an autophagy inhibitor) and inhibited by Rap (an autoph-agy inducer ) .ox-LDL induced autophagy in the macrophages as assessed by beclin-1 upregulation and frequent granulation of LC3, which were inhibited by 3-MA and promoted by Rap.Interestingly, 3-MA enhanced, while Rap blocked, the CHOP upregulation induced by ox-LDL.Moreover , PBA ( endoplasmic reticulum stress inhibitor ) significantly inhibited ox-LDL-induced GRP78 upregulation and autophagy as determined by the attenuation of beclin-1 upregulation and frequent granula-tion of LC3.CONCLUSION: Endoplasmic reticulum stress mediates ox-LDL-induced autophagy in macrophages , and moderates activation of autophagy may protect macrophages from ox-LDL-induced apoptosis by inhibiting CHOP expression .