Sixteen triterpenoid saponins (1-16) were isolated from the stems of Clematis parviloba, including a new compound, parvilobaside A (1), which was established as 23-O-acetyl-hederagenin-3-O-beta-D-ribopyranosyl-(1 ->> 3)-alpha-L-rhamnopyranosyl-(1 ->> 2)-alpha-l-arabinopyranoside on the basis of various spectroscopic techniques and chemical evidences. Among the isolated compounds, clematoside S (2) and alpha-hederin (4) showed moderate cytotoxic activities against four human tumor cell lines (HCT-8, Bel-7402, BGC-823, and A-2780) with IC(50) values in the range of 1.44-6.86 microg/ml.