Taxus yunnanensis W. C. Cheng & L. K. Fu, synonym of Taxus wallichiana Zucc.var.wallichiana. Genus:Taxus; Family:Taxaceae. Amentotaxus yunnanensis is a species of conifer in the Taxaceae family. It is found in China and Vietnam. It is threatened by habitat loss. The H2O, H2O/MeOH (1:1) extracts from the wood of Taxus yunnanensis showed a remarkable inhibitory effect on induced histamine release from the human basophilic cell line, KU812. The eleven constituents purified from the wood extracts of Taxus yunnanensis were tested by an in vitro histamine release inhibition assay. Among them, secoisolarciresinol and taxiresinol were found to show inhibitory activities. A new neolignan, 2-[2-hydroxy-5-(3-hydroxypropyl)-3-methoxyphenyl]-1-(4-hydroxy-3-methoxyphenyl)propane-1,3-diol, was isolated from the wood of Taxus yunnanensis. Two new taxane diterpenoids as well as a known one, taxayunnansin A, were isolated from the roots of Taxus yunnanensis. One of the new compounds was identified as a unique taxane with a 2,20-oxetane ring.