One novel p-terphenyl compound, polyozellic acid (1), and its acetone adduct (3), along with a known p-terphenyl compound, thelephoric acid (2), were isolated from the mushroom Polyozellus multiplex. Their molecular structures were determined by spectroscopic analysis, X-ray crystallographic analysis, and chemical modification. In some assays related to angiogenesis, compounds 1 and 2 in particular showed inhibitory effects on proliferation, tubule formation, and invasion of human umbilical vein endothelial cells. The quinone moiety within these molecules possibly contributes to their antiangiogenesis activity.