Growing evidence indicates that oxidized low density Iipoprotein (LDL) may promote atherogenesis. Therefore, inhibition of LDL oxidation may impede this process. The effect of chitin sulfate on the susceptibility of human low density lipoprotein (LDL) to macrophages-induced oxidation was investigated by monitoring a thiobarbituric acid reactive substance (TBARS). Chitin sulfate inhibited LDL oxidation by macro phages in a dose dependent manner, with a 50-100μM, as assessed by TBARS assay. Chitin sulfate, at 100 μM, almost completely inhibited the macrophage-induced increase in electrophoretic mobility of LDL. Also, chitin sulfate almost completely inhibit O₂^- at concentration of 100 μM. These observations suggest that chitin sulfate might be an effective in prevention of atherosclerosis.