Solid-state polycondensation of natural aldopentoses and 6-deoxyaldohexoses was found to take place in the presence of H3PO4 (5 mol%) at 100-110 degrees C under a N-2 flow, giving highly branched polysaccharide (Conv. 47-81%, M-w= 2700-12000, M-n = 1400-2900); the reaction mixtures were powdery throughout the polymerization. The product polysaccharide was per-O-methylated and subjected to the structure analyses. The acid-hydrolysis, which gave a variety of the partially O-methylated monosaccharides, suggested that the product polysaccharides proved to have highly branched structures consisting of both furanose and pyranose units. MALDI-TOF mass analysis revealed that the 1,4-anhydride terminal unit was formed and participated to the polymerization. (c) 2005 Elsevier Ltd. All rights reserved.