A new triterpenoid saponin named clematichinenoside AR(2), along with the six known compounds, was isolated and characterized from Clematis chinensis Osbeck (Ranunculaceae), a commonly used traditional Chinese medicine with anti-inflammatory and anti-rheumatoid activities. The structure of the new saponin was elucidated as 3-O-beta-[(O-alpha-L-rhamnopyranosyl-(1 --> 6)-O-beta-D-glucopyranosyl-(1 --> 4)-O-beta-D-glucopyranosyl-(1 --> 4)-O-beta-D-ribopyranosyl-(1 --> 3)-O-alpha-L-rhamnopyranosyl-(1 --> 2)-alpha-L-arabinopyranosyl)oxy]olean-12-en-21alpha-hydroxy-28-oic acid-O-alpha-L-rhamnopyranosyl-(1 --> 4)-O-beta-D-glucopyranosyl-(1 --> 6)-beta-D-glucopyranosyl ester (1) by spectral analysis and chemical methods. The effects of two major saponins (clematichinenosides AR and AR(2)) on the secretion of TNF-alpha in murine peritoneal macrophages induced by lipopolysaccharides were further investigated. The result indicated that a majority of triterpenoid saponins of this herb may be useful in the exploration of lead compounds for the treatment of some autoimmune diseases.