Antrodia camphorata is well known in Taiwan as a traditional Chinese medicine. In this study, we have investigated the antioxidant properties of a fermented culture broth of Antrodia camphorata (FCBA) and the aqueous extracts of mycelia from Antrodia camphorata (AEMA) on the oxidative modification of human low-density lipoproteins (LDL), as induced by either copper sulfate (CuSO(4)) or 2,2'-azo-bis(2-amidinopropane) hydrochloride (AAPH). Under such oxidant stress, FCBA and AEMA appear to possess antioxidant properties with respect to oxidation of LDL in a time-and concentration-dependent manner, as assessed by inhibition of thiobarbituric acid-reactive substances (TBARS) formation, conjugated diene production, and cholesterol degradation of oxidized LDL. In addition, both FCBA and AEMA exhibited a remarkable ability to rescue the relative electrophoretic mobility and fragmentation of the Apo B moiety of the oxidized LDL. Furthermore, FCBA and AEMA effectively protected the endothelial cells from the damaging effects of the CuSO(4)-oxidized LDL. Our findings suggest that the antioxidant properties of Antrodia camphorata may also provide effective protection from atherosclerosis.