The two hemicellulosic fractions were subsequentially extracted with 5% and 8% NaOH aqueous solution at a solid to liquid ratio of 1:25 (g mL⁻¹) at 50 °C for 3 h from the water, 1 and 3% NaOH-treated sugar cane bagasse, and subfractionated into six preparations by a graded ethanol precipitation method at concentrations of 15%, 30% and 60% (v/v). Sugar composition and molecular weight analysis showed that, with an increasing concentration of ethanol, hemicellulosic subfractions with both higher Ara/Xyl ratios and higher molecular weights were obtained. In other words, with an increasing ethanol concentration from 15% to 60%, the Ara/Xyl ratios increased from 0.043 in H₁ to 0.088 in H₃ and from 0.040 in H₄ to 0.088 in H₆, and the weight-average molecular weights of hemicellulosic subfractions increased from 42 430 (H₁) to 85 510 (H₃) g mol⁻¹ and from 46 130 (H₄) to 64 070 (H₆) g mol⁻¹, respectively. The results obtained by the analysis of Fourier transform infrared, sugar composition, and ¹H and ¹³C nuclear magnetic spectroscopy showed that the alkali-soluble hemicelluloses had a backbone of xylose residues with a β-(1→4)-linkage and were branched mainly through arabinofuranosyl units at C-2 and/or C-3 of the main chain, whereas the differences may occur in the distribution of branches along the xylan backbone.