A new diterpenoid trisaccharide, smithoside A, was isolated from Aster smithianus. Itsstructure was identified as pimar-15 (16)-β-en-3β, 8β, 11α-triol-3-O-β-D-glucopyranosyl (1→3)-[β-glucopyranosyl (1→2)]-β-D-glucopyranoside on the basis of the spectral and chemical methods. A new diterpenoid trisaccharide, smithoside A, was isolated from Aster smithianus. It has been identified as pimar-15 (16) -β-en-3β, 8β, 11α-triol-3-O-β-D-glucopyranosyl ) - [β-glucopyranosyl (1 → 2)] - β-D-glucopyranoside on the basis of the spectral and chemical methods.