In this study, we invest gated the antioxidative functions of carotenes (CARs) against the peroxidation of lipids initiated by nitrogen dioxide-Using density functional theory. The hydrogen-atom transfer (HAT), radical adduct formation (RAF), and electron transfer (ET) mechanisms Were investigated. We chose beta-carotene (beta-CAR) and lycopene (LYC) and compared their NO2 center dot initiations, and peroxidations With those of linoleic acid (LAB), the Model of the lipid. We found that for CARs ET is more likely to occur in the most polar (water) environment than are HAT and RAF. In less polar environments, CABs react more readily with NO2 center dot via HAT and RAF than does the lipid model, LAH. Comparatively, reaction barriers for the RAF between CARs and NO2 center dot! are smaller than those for the HAT. The additions of O-2 to the radical intermediates O2N-CAR(center dot) and CAR(-H)(center dot) involve sizable barriers and are endergonic. Other than HAT of LAH, we revealed that lipid peroxidation is likely to be initiated by NO2 addition and the subsequent barrierless addition of O-2. Finally, LYC, is a more effective antioxidative agent against NO2 center dot-initiated lipid peroxidation than is beta-CAR.