Oxymatrine, a quinolizidine alkaloid isolated from the traditional Chinese herb Sophora flavescens Aiton, has been demonstrated to exert anti鈥慽nflammatory and atherosclerotic effects, but the molecular mechanism has yet to be elucidated. Accumulating evidence indicates an important role of NLR family pyrin domain containing 3 (NLRP3) inflammasome鈥憁ediated pyroptosis in the pathogenesis of atherosclerosis. The present study was undertaken to investigate whether oxymatrine attenuates oxidized low鈥慸ensity lipoprotein (ox鈥慙DL)鈥慽nduced human umbilical vein endothelial cell (HUVEC) injury, an in vitro cell model of atherosclerosis, by inhibiting NLRP3 inflammasome鈥憁ediated pyroptosis, and elucidate the role of the sirtuin (SIRT)1/nuclear factor鈥慹rythroid 2鈥憆elated factor 2 (Nrf2) signaling pathway in this process. Cell viability and cytotoxicity were detected by CCK鈥? assay and a lactate dehydrogenase (LDH) assay kit. Cell apoptosis was detected by flow cytometry. Reactive oxygen species (ROS) generation was detected using a ROS assay kit. The malondialdehyde (MDA) content, mitochondrial membrane potential (MMP) level, superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GSH鈥慞x) activities were determined using commercial kits. The inflammatory cytokines levels were measured by ELISA and protein expression was monitored by western blot analysis. The results revealed that oxymatrine alleviated ox鈥慙DL鈥慽nduced cytotoxicity and apoptosis. Concurrently, oxymatrine inhibited ox鈥慙DL鈥慽nduced NLRP3 inflammasome鈥憁ediated pyroptosis in HUVECs, as evidenced by the significant decreases in the expression of NLRP3, apoptosis鈥慳ssociated speck鈥憀ike protein containing a C鈥憈erminal caspase recruitment domain (ASC), cleaved caspase鈥?, interleukin (IL)鈥?beta and IL鈥?8 in HUVECs. In addition, NLRP3 siRNA transfection efficiently suppressed ox鈥慙DL鈥慽nduced pyroptosis and HUVEC injury. Furthermore, oxymatrine promoted SIRT1/Nrf2 signaling pathway activation in HUVECs subjected to ox鈥慙DL treatment, and SIRT1 deficiency induced by SIRT1 siRNA transfection abolished the protective effect of oxymatrine against ox鈥慙DL鈥慽nduced injury. SIRT1 siRNA also mitigated the oxymatrine鈥慽nduced decreases in ROS generation and MDA content, and the increases in MMP as well as the activities of SOD, CAT and GSH鈥慞x in HUVECs. Moreover, SIRT1 siRNA transfection blocked the inhibitory effect of oxymatrine on NLRP3 inflammasome鈥憁ediated pyroptosis in ox鈥慙DL鈥憈reated HUVECs. Collectively, these results indicated that oxymatrine may attenuate ox鈥慙DL鈥慽nduced HUVEC injury by inhibiting NLRP3 inflammasome鈥憁ediated pyroptosis via activating the SIRT1/Nrf2 signaling pathway.