Amauroderma rugosum fruiting bodies possess excellent cardiovascular benefits, including antioxidative, antihyperlipidemic, antihypertensive, antiinflammatory, anti-platelet aggregation, and antithrombotic effects. In this article, we describe our investigations of the in vitro antioxidant activity and in vitro antiatherosclerotic potential through inhibitory effects on low-density lipoprotein (LDL), LDL peroxidation, and 3-hydroxy3-methylglutaryl-coenzyme A (HMG-CoA) reductase catalytic activity using various fruiting body extracts partitioned with an organic solvent. Among 5 extracts/fractions tested, the semipolar ethyl acetate (EA) fraction demonstrated good antioxidant capacity based on total phenolic content, 2,2-diphenyl-1-picrylhydrazyl free radical scavenging, ferrous ion-chelating ability, cupric ion-reducing antioxidant capacity, and lipid peroxidation assays. The EA fraction also showed the strongest inhibitory effect on Cu2+-induced LDL oxidation via thiobarbituric acid reactive substances formation and HMG-CoA reductase activity. Chemical analysis conjointly identified 10 phenolic compounds (4 benzoic acid derivatives, 3 flavonoids, 1 cinnamic acid, 1 hexahydroxydiphenic acid dilactone, and 1 xanthone derivative), some of which play pivotal roles in arresting the physiopathogenesis of atherosclerosis, thereby attenuating the risk of cardiovascular events occurring.