In order to study the effect of pcsk9 siRNA on THP-1 derived macrophages apoptosis induced by oxLDL，THP-1 derived macrophages were induced to differentiate into macrophages by PMA treatment for 24 h. The experiments were designed as follows: cells were incubated with oxLDL with a concentration of 0, 25, 50, 75, 100 mg/L for 48 h respectively. The apoptosis of THP-1 derived macrophages was observed by staining with Hoechst33258. The expression of pcsk9 was analyzed by reverse transcription polymerase chain reaction and Western blot. The siRNAs for pcsk9 gene were designed and synthesized，then transfected into THP-1 derived macrophages by positive ion liposome Lipofectamine 2000. Transfection efficiency was assessed by fluorescence microscope assay. RT-PCR and Western blot were conducted to detect the expression of pcsk9 after 24 h, 48 h respectively. The most efficient siRNA was selected to transfect into THP-1 derived macrophages. 24 h after transfection, cells were treated with oxLDL for 48 h, and then Hoechst 33258 staining. The results showed that the number of cells with nuclear condensation induced by 75 mg/L oxLDL increased significantly. In THP-1 derived macrophages, pcsk9 was upregulated with increasing concentration of oxLDL, while 75 mg/L oxLDL increased significantly. The RNA interference experiment showed that siRNA was successfully transfected into cells and 80 nmol/L as most effective dose of siRNA was selected by RT-PCR and Western blot. Compared with control, the suppression of apoptosis in THP-1 cells transfected with 80 nmol/L of siRNA for 24 h and incubated with 75 mg/L of oxLDL for another 48 h was detected by Hoechst 33258 staining and flow cytometer. Together, these results reveal the expression of pcsk9 mRNA and protein were increased by oxLDL in a concentration-dependent manner. Expression of pcsk9 gene could be effectively suppressed by siRNA. The apoptosis of THP-1 derived macrophages induced by oxLDL could be effectively suppressed by pcsk9 siRNA.