Objective:To investigate the effects of PCSK9 siRNA on CD36,SR-A1 and SR-B1 expressions in THP-1 derived macrophages. Methods:The siRNA for PCSK9 gene were transfected into THP-1 derived macrophages using positive ion liposome Lipofectamine 2000. Transfection efficiency was assessed by fluorescence microscope assay. The expression of PCSK9 in THP-1 derived macrophages at 24 h after transfection was detected by RT-PCR and Western blot. The most efficient siRNA was selected for transfection. At 24 h after transfection,macrophages were treated with ox-LDL for another 24 h. Then the intracellular lipid accumulation was observed by oil red O staining,and expressions of CD36 mRNA,SR-A1 mRNA and SR-B1 mRNA were detected by RT-PCR. Results:siRNA of 80 nmol/L showed the strongest inhibition for the gene expression of PCSK9,and ox-LDL-induced accumulation of cholesterol and upregulation of CD36 mRNA expression in THP-1 derived macrophages decreased by application of PCSK9 siRNA(P < 0.05). However,PCSK9 siRNA caused no effect on ox-LDL-induced upregulation of SR-A1 mRNA and SR-B1 mRNA expression in macrophages. Conclusion:PCSK9 may be involved in atherosclerosis development by inhibiting the expression of CD36.