Abstract: To make bamboo cellulose efficiently utilized, structural characterizations of three fractional celluloses isolated by alkaline hydrogen peroxide from defatted bamboo fiber were studied. The results demonstrated that weight-average relative molecular weight (MW) of cellulose gradually decreased because of the deepening fractured-degree of cellulose molecular chain with the increasing of fractional grade. There didn’t appear the absorbance spectra relative to lignin and hemicellulose in the FT-IR pictures owing to the highly purities of three fractional celluloses. After fractionating, there occurred some great changes for the structure of three fractional celluloses, so many holes and cannelures were distributed in the loose surface of cellulose fibers. The length and crystalline degree of the first, second and third fractional cellulose decreased in proper order, while the cellulose hydrolysis ratio was just the reverse. Thus it can be seen that the processing and application characteristics of the first, second and third fractional cellulose could be improved.