A triterpenoid saponin (1) was obtained from the stem barks of Albizia julibrissin Durazz. Its structure was elucidated as 3-O-[beta-D-xylopyranosyl-(1 --> 2)-alpha-L-arabinopyranosyl-(1 --> 6)-beta-D-glucopyranosyl]-21-O-[(6S)-2-trans-2-hydroxymethyl-6-methyl-6-O-beta-D-quinovopyranosyl-2, 7-octadienoyl]-16-deoxy-acacic acid 28-O-beta-D-glucopyranosyl-(1 --> 3)-[alpha-L-arabinofuranosyl-(1 --> 4)]-alpha-L-rhamnopyranosyl-(1 --> 2)-beta-D-glucopyranosyl ester (1), named as Julibroside J26, based on the chemical and spectral methods.