Background <p>Atherosclerosis (AS), a chronic inflammatory disease of the arterial wall, remains a dominant cause of death and disability globally. Quercetin has been evidenced to be effective against AS, but the exact mechanisms are still largely unclear.</p> Methods <p>Oxidized low-density lipoprotein (ox-LDL)-induced human aortic endothelial cells (HAECs) and mouse RAW264.7 macrophages were established, with quercetin treatment or p16, p21 or SERPINE1 siRNA transfection. Cellular senescence was assessed by SA-β-gal staining and detection of cellular senescence markers. Cell cycle, apoptosis and intracellular ROS were detected by flow cytometry, with cell proliferation by CCK-8. Lipid accumulation was assessed utilizing oil red O staining. Through transmission electron microscope, autophagosomes and mitochondria were investigated, with detection of autophagy markers. Finally, AS models of ApoE^−/− mice were established through feeding high-fat diet, and the effect of quercetin on alleviating AS progression was investigated.</p> Results <p>Quercetin protected HAECs from ox-LDL-elicited senescent phenotype, growth arrest and apoptosis and promoted cell viability in a concentration-dependent fashion. Furthermore, quercetin alleviated ox-LDL-elicited cellular senescence, ROS and lipid accumulation in macrophages. In ox-LDL-induced HAECs or/and macrophages, quercetin down-regulated the expression of p16, p21, p53 and SERPINE1, elevated p-AMPK/AMPK levels and decreased p-mTOR/mTOR levels, and these effects of quercetin were ameliorated by SERPINE1 knockdown. In AS mouse models, quercetin treatment alleviated AS progression.</p> Conclusion <p>Our findings proposed a novel anti-atherosclerotic mechanism of quercetin by mitigating ox-LDL-elicited senescent phenotype of aortic endothelial cells and macrophages by regulating p16/p21, p53/SERPINE1, and AMPK/mTOR pathways.</p>