A new taraxastane-type triterpenoid glycoside, clematiunicinoside I (1), together with four known ones (2-5), was isolated from the roots of Clematis uncinata. The structure of the new compound was elucidated on the basis of spectroscopic analyses and acid hydrolysis. The cytotoxic activities of all the compounds against caski cervical cancer (Caski) cells were evaluated. This is the first report of the presence of taraxastane-type triterpenoid glycoside in the genus Clematis.