Abstract: Objective: To investigate the effect of monotropein (MON) on macrophage polarization and the formation of THP-1 derived foam cells. Methods: THP-1 cells were incubated with 100 ng/mL phorbol 12-myristate 13-acetate (PMA) for 48 hours to induce M0 macrophages, which were identified by flow cytometry. Foam cells were induced by treating macrophages with different concentrations of oxidized low-density lipoprotein (ox-LDL) (0 μg/mL, 25 μg/mL, 50 μg/mL, 100 μg/mL, 150 μg/mL) for different ox-LDL intervention times (0 h, 3 h, 6 h, 12 h, 24 h). Macrophages were intervened with ox-LDL or MON, and cell viability was assessed using CCK-8. The experimental groups were divided into control group, ox-LDL group, and ox-LDL+MON group. Oil Red O staining was employed to observe the lipid engulfment of cells in each group. Western blotting and reverse transcription-quantitative PCR (RT-qPCR) were utilized to evaluate the polarization of macrophages and the outcomes of signaling pathways associated with ferroptosis. Results: The ox-LDL increased iNOS and TNF-α protein expression in a concentration-and time-dependent manner. The ox-LDL significantly reduced cell viability, which could significantly be restored by 200 μmol/L MON, but would be decreased when the concentration was up to 1000 μmol/L MON. A large number of obvious ox-LDL-induced intracellular lipid droplets were observed in the cells, and the amount of lipid droplets in the cells were markedly reduced with MON treatment. Compared with the control group, ox-LDL-induced macrophages showed increased CD86 mRNA and iNOS protein expression levels and decreased CD206 mRNA, Arg-1, SLC7A11, and GPX4 protein expression levels, while MON intervention decreased CD86 mRNA and iNOS protein expression levels and increased Arg-1, SLC7A11, and GPX4 protein expression levels (all P＜0.05). Conclusion: MON inhibits ox-LDL-induced foam cell formation and enhances cell viability by reducing M1 polarization and promoting M2 polarization in macrophages, which may be associated with inhibition of ferroptosis.