Abstract: The function of xylooligosaccharides is better than other drugs or foods of oligosaccharides. Xylooligosaccharides were distilled from the wastwater in the process of biomass to fuel ethanold using themethod of slow-dynamics. Additionally, their purity and average molecular weights were measured using capillary electro-chromatography and polyacrylamide gel electrophoresis. The results show that their content reaches about 90% and average molecular weights are 300-600.