It has been reported that green tea consumption reduces the risk of coronary artery disease and cardiac events. Catechin is a major constituent of Japanese green tea and an antioxidant. Lipids and oxidization of low-density lipoprotein cholesterol (LDL-C) play important roles in atherosclerosis. Therefore, we evaluated the effect of catechin intake on the lipid profile and plasma oxidized LDL. The study population consisted of 40 healthy adult volunteers (10 men, 30 women). Catechin was extracted from green tea leaves. The subjects were randomly divided into two groups, a catechin group (n = 29) and a control group (n = 11). In the catechin group, catechin (500 mg: equivalent to 6 or 7 cups of green tea) was administered orally. Venous blood samples were obtained before eating a meal at the start and after 4 weeks without any lifestyle modification. Plasma oxidized LDL assay was performed with a sandwich-type enzyme immunoassay using anti-oxidized phosphatidylcholine monoclonal antibody. The baseline lipid profiles and tea consumptions were similar between the two groups. Plasma oxidized LDL was significantly decreased after catechin administration (from 9.56 +/- 9.2 to 7.76 +/- 7.7 U/mL, P = 0.005), while plasma LDL-C, triglyceride, and HDL-C concentrations did not change. Catechin decreased the plasma oxidized LDL concentration without significant change in plasma LDL concentration. The mechanism of the beneficial effects of green tea on coronary artery disease might result from a decrease in plasma oxidized LDL.