We examined the beneficial effects of an active principle in kimchi, 3-(4'-hydroxyl-3',5'-dimethoxyphenyl)propionic acid (HDMPPA), on atherogenesis in apolipoprotein E knockout (apoE KO) mice. ApoE KO mice were fed an atherogenic diet containing 1% cholesterol (control group) with an intraperitoneal injection of chemically synthesized HDMPPA (10 mg/kg/day) (HDMPPA group) for 8 weeks. The aortic sinus atherosclerotic lesion size in the HDMPPA group (n = 10) was significantly smaller (control vs. HDMPPA, 280,790 vs. 165,409 microm(2), P < .001). The level of reactive oxygen species (ROS) in the HDMPPA group was lower by 14%, compared with the control group (P < .05). Aortic NADPH oxidase activity was significantly lower in the HDMPPA group than in the control group. HDMPPA suppressed the mRNA expression of p47phox and rac-1 of NADPH oxidase by 27.2% and 46.0%, respectively, compared with values of the control group. In conclusion, HDMPPA in kimchi may attenuate atherosclerosis in apoE KO mice through retardation of ROS generation via down-regulating the mRNA expression of p47phox and rac-1, which are the components of NADPH oxidase.