Oxidation of LDL induced by free radicals proceeds by a chain mechanism to give phosphatidylcholine hydroperoxides and cholesteryl ester hydroperoxides as the major primary products. In addition, apolipoprotein B100 is also oxidized. Various antioxidants suppress the oxidative modification of LDL. Water-soluble radical-scavenging antioxidants such as vitamin C and uric acid act as the first defense to suppress the chain initiation. Lipophilic radical-scavenging antioxidants in LDL such as vitamin E and ubiquinol scavenge radicals attacking from outside and also within the LDL. The overall importance and potency of antioxidants depend not only on chemical reactivity but also on the physical factors such as location and mobility at the microenvironment in LDL.