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Objective To investigate the protective mechanism of PCSK9 inhibitor against oxidative low-density lipoprotein (ox-LDL) induced injury of human umbilical vein endothelial cells (HUVECs). Methods HUVECs in logarithmic growth phase were divided into Control group (normal culture group), ox-LDL group (induced by 50 mg/L oxLDL for 24 h) and PCSK9 inhibitor groups (low, medium and high dose of PCSK9 inhibitor). The low, medium and high dose of PCSK9 inhibitor groups were treated with 5, 10 and 20 µmol/L PCSK9 inhibitors for 24 h and then induced by 50 mg/L ox-LDL for 24 h. Cell activity was detected by CCK-8 assay, and cell survival rates were calculated. Transcription and secretion levels of tumor necrosis factor-α (TNF-α), interleukin 6 (IL-6) and monocyte chemotactic protein-1 (MCP-1) in supernatant of cell culture were determined by quantitative real time polymerase chain reaction (qPCR) and enzyme-linked immunosorbent assay (ELISA). Cell apoptosis was detected by flow cytometry. The expression levels of apoptosis-related proteins (Bax, Bcl-2, Cleaved-Caspase-3) and nuclear factor-κB (NF-κB) signaling pathway related proteins were detected by Western blot assay. Results Compared with the Control group, the cell survival rate was decreased, transcriptional and secretion levels of TNF-α, IL-6, MCP-1 were increased, apoptosis rate increased, pro-apoptotic proteins (Bax and cleaved Caspase-3) up-regulated, anti-apoptotic protein Bcl-2 down- regulated and phosphorylated NF-κB (p-NF-κB) expression increased in ox-LDL group. Meanwhile, the expression of NF-κB was up-regulated in the nucleus and down regulated in cytoplasm. Compared with ox-LDL group, the survival rates were increased in medium and high dose PCSK9 inhibitor groups after treatment with PCSK9 inhibitor. The transcription and secretion levels of TNF-α, IL-6, MCP-1 and apoptosis rate decreased. The results of Western blot assay showed that the expression levels of Bax and cleaved-Caspase-3 downregulated, Bcl-2 up-regulated and p-NF-κB decreased. PCSK9 inhibitors down-regulated the expression of NF-κB in the nucleus and up-regulated the expression of NF-κB in cytoplasm of HUVECs induced by ox-LDL (P < 0.05). Conclusion PCSK9 inhibitors can inhibit ox-LDL induced inflammatory response and cell apoptosis in HUVECs and play a protective role. [ABSTRACT FROM AUTHOR]