Acanthoic, continentalic and kaurenoic acids are bioactive diterpenoids that are structural isomers isolated from Acanthopanax species. Due to the interest in their potent biological activity, an analytical method of diterpenoids was developed for the quality control and the classification of Acanthopanax species. Capillary electrophoresis was used to separate and quantify the isomers. The three compounds were successfully separated from each other and from the matrices in the extracts of leaves, stems and roots of Acanthopanax species. The contents of acanthoic, continentalic and kaurenoic acids showed taxonomical differences in Acanthopanax species. Relatively higher concentrations of diterpenoids were found from A. koreanum and A. trifoliatus, while only trace amounts were found from the four other species tested: A. senticosus, A. senticosus f. inermis, A. chiisanensis, and A. divaricatus var. albeofructus. The contents of diterpenoids in association with lignans and triterpenoids in the Acanthopanax species could provide a chemotaxonomical index able to be used in the classification and discrimination of the species.