The dewaxed sample from Triploid of Populus tomentosa Carr. was extracted by using organic alkaline solvent (Dimethylformamide, DMF) via hydrothermal pretreatment. Neutral sugar compositions and molecular weight analysis demonstrated that the hemicellulosic fractions with a higher Uro/Xyl ratio, namely the more branched hemicelluloses, had higher molecular weights. Interestingly, these results were different from the previous report, in which the ratio of Uro/Xyl in the water-soluble hemicellulosic fraction was more than that of the alkali-soluble hemicellulosic fraction. Spectroscopy (FUR, H-1 NMR, C-13 NMR, and HSQC) analysis indicated that the hemicellulosic fractions were mainly composed of (1 -> 4)-linked alpha-D-glucan from starch and (1 -> 4)-linked beta-D-xylan attached with minor amounts of branched sugars from hemicelluloses. In addition, thermal analysis implied that linear hemicelluloses showed more thermal stability than the branched ones during pyrolysis. (C) 2012 Elsevier Ltd. All rights reserved.