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A pectic polysaccharide (CPP1b) was at first isolated from Codonopsis pilosula. Sugar analysis revealed that CPP1b is composed of rhamnose (Rha), arabinose (Ara), galactose (Gal) and galacturonic acid (GalA) with a molar ratio of 0.25:0.12:0.13:2.51. The result of esterification assay showed that about 46.7±0.4% of carboxylic groups in GalA residues existed as methyl ester. Combined with chemical and spectroscopic analyses, a preliminary structure of CPP1b was proposed as follows: 1,4-linked α-D-GalpA and 1,4-linked α-D-GalpA6Me interspersed with rare 1,2-linked β-L-Rhap, 1,2,6-linked α-D-Galp and terminal α-L-Arap. CPP1b had an average molar mass and root-mean square radius (RMS) of 1.45×10(5) Da and 29.7 nm, respectively, and presented a linear random coil conformation in 0.9% NaCl. The ultrastructure of CPP1b was further investigated by transmission electron microscope (TEM) and scanning electron microscope (SEM). CPP1b exhibited obvious cytotoxicity to human lung adenocarcinoma A549 cells in a dose- and time-dependent manner., (Copyright © 2013 Elsevier Ltd. All rights reserved.)