Forty hyperlipidemic patients, smokers and non-smokers, were studied. Subjects received 15 g young barley leaf extract (BL) or 60 g adlay daily for four weeks. The overnight fasting blood samples were drawn immediately prior to and after four weeks of supplementation. Blood samples were analyzed for plasma lipid profiles and their susceptibility to low-density lipoprotein (LDL) oxidation. The plasma total and LDL-cholesterol (LDL-C) levels were reduced following treatment with either BL or adlay. Furthermore, the lag phase of LDL oxidation increased after BL or adlay supplementation. However, it seemed that BL had stronger antioxidative effect on the prevention of LDL oxidation than adlay. These results also indicated that the antioxidative effect was less pronounced in smokers compared to non-smokers. Therefore, supplementation with BL or adlay can decrease plasma lipids and inhibit LDL oxidation, which may protect against atherosclerosis in hyperlipidemic smokers and/or non-smokers.