Thelephora vialis is a mushroom that grows in symbiosis with pine trees in Yunnan, China, a place known to have some of the richest and most diverse bioresources in the world. This is one of the most favored edible mushrooms, due to its flavor. Our screening for bioactive compounds from these mushrooms isolated a novel potent antioxidant, vialinin A, together with known compounds, from the dry fruiting bodies of T. vialis. Vialinin A is a terphenyl derivative and was elucidated by spectroscopic and chemical methods. Vialinin A showed anti-allergic activities, inhibition of beta-hexosaminidase, tumor necrosis factor (TNF)-alpha, interleukin 4 and monocyte chemotactic protein 1 release from RBL-2H3 cells, whereas atromentin and an inseparable mixture of ganbajunins D and E showed no such effects. Vialinin A displayed potent inhibition of TNF-alpha production from RBL-2H3 cells (IC50, 0.09+/-0.01 nM), indicating stronger inhibition than tacrolimus for organ transplantation (IC50, 0.25+/-0.03 nM). The potent inhibitory activities of these compounds against TNF-alpha production indicate promising new candidates for anti-allergic agents.