Abstract: AimTo investigate the chemical constituents of seeds of Koelreuteria paniculata Laxm., components were separated by means of solvent extraction and chromatography on C₁₈, the structure of compound was determined by spectral analysis and chemical evidences. One saponin was obtained and identified as 28-O-isopentyryl-3β,16α,22β,28-tetrahydroxyl-oleanane-3-O-［α-L-rhamnopyranosyl-(1→3′)-β-D-galactopyranosyl-(1→4′)］-β-D-galacturonopyranoside, named paniculata saponin C. This saponin is a new compound.