Seven residual hemicellulosic preparations (19.6-45.0% of the original hemicelluloses) were extracted from wheat straw pre-treated with various organic solvents using 1.8% H2O2-0.18% cyanamide at 50 degrees C and pH 10.0 for 4 h. Their chemical compositions and physicochemical properties were determined using GC, HPLC, GPC, FT-IR and (NMR)-N-13 spectroscopy. The results indicated that all the residual hemicellulosic preparations were heteropolysaccharides containing xylose, glucose, arabinose, galactose, mannose, rhamnose and 4-O-methyl-alpha-D-glucopyranosyluronic acid. The predominant monosaccharide was xylose, ranging between 67.7% and 81.9% of the total neutral sugars, composed mainly of L-arabino-(4-O-methyl-D-glucurono)-D-xylan. The content of contaminant lignin in the isolated residual hemicelluloses was 2.89-5.31%. The M-w values of the two residual hemicellulosic preparations H-6 and H-7 (42,7 10 and 44,080 g mol(-1), respectively) obtained from the aqueous-alcohol pre-treated straw were much higher than those of H-1-H-5 (12,980-15,950 g mol(-1)) extracted from the organic acid pre-treated straw. (c) 2004 Elsevier Ltd. All rights reserved.