A new catechin derivative, catechin-5-O-(6-O-galloyl-β-glucopyranoside) (2), together with ten known flavonoids, was isolated from the leaves and stems of Taxillus theifer (Hayata) H. S. Kiu. T. theifer is a shrub parasitizing on different species of plants. Three samples of T. theifer on various host plants were collected and their chemical constituent variations were identified and estimated by HPLC/UV methods. A comparison of the constituents from T. theifer parasitizing on different host trees demonstrated that catechin (1), quercetin-3-O-(6-O-galloyl-β-glucopyranoside) (3), quercetin-3-O-β-glucopyranoside (5), and quercetin-3-O-β- glucuronide (6) were the major components in the title plant irrespective of the host tree. However, the content of some components
varies for each sample.