Abstract: To make bamboo cellulose efficiently utilized, structural characterizations of three hemicelluose fractions isolated by alkaline hydrogen peroxide from defatted bamboo fiber were studied. The results demonstrated that the purity of three fractional hemicelluloses is very high except that the first fractional hemicellulose contains only a little lignin. The three fractional hemicelluloses contain four structural units of xylose, glycuronate, arabinose and galactose, and could be xylan-hemicellulose because of the highest content of xylose up to about 50%. The three fractional hemicelluloses are non-crystal and have great differences in physical structures. The first fractional hemicellulose includes only a sphere, while the second and third fractional hemicelluloses contain irregular polyhedron and white nebulous object. Weight-average relative molecular weight (MW) of hemicellulose gradually decreased because of the deepening fractured-degree of hemicellulose molecular chain with the increasing of fractional grade.