A new class of ellagitannins, castanopsinins A-H (1, 6, 25, 27, 32, 42, 47 and 51), containing a triterpenoid glycoside core, have been isolated from the leaves of Castanopsis cuspidata var. sieboldii NAKAI (Fagaceae). On the basis of spectroscopic and chemical data these compounds have been characterized as 3, 23-(R)-(1), 24-O-galloyl-3, 23-(R)-(6), 2, 3-(R)-(25), 3, 23-(S)-(27), 3, 24-(S)-(32), 24-O-galloyl-3, 23-(S)- (42), 3'-O-galloyl-23, 24-(R)- (47) and 24, 3'-di-O-galloyl-3, 23-(R)-hexahydroxydiphenoyl (51) 2α, 3β, 23, 24-tetrahydroxyolean(urs)-12-en-28-oic acid 28O-β-D-glucopyranosides. In addition, separation of structural isomers consisting of a mixture of oleanane- and ursane-type triterpenoids was successfully achieved.