Separation and characteristics of hemicellulose, lignosulfonate, and saccharide fractions of NSSCP spent liquors has been studied. The samples of spent liquor used were obtained by cooking Japanese birch wood chips for 1-6hrs. In all cases, the temperature was raised to 170°C (highest level) in 1 hr. The resulting liquor was concentrated to a solid content of 23% for use in the experiments on separation. The results are summarized as follows : The three fractions named above can be separated by adding acetone to the concentrated liquor. The optimum amount of acetone for the separation of hemicellulose fraction is determined by both water content and inorganic material content of the concentrated liquor, whereas the optimum amount for the separation of lignosulfonate and saccharide fractions, namely an additional amount of acetone to be used after the removal of hemicelluloses, is determined only by the water content of the same liquor.In all the spent liquor samples studied, the hemicellulose fraction capable of separation by acetone amounts to about 10% of the total organic material content of the liquor. The intrinsic viscosity of this fraction is almost independent of the period of cooking at the maximum temperature, whereas the carbohydrate composition varies with cooking time. The proportion of the five component sugars, galactose, glucose, mannose, arabinose, and rhamnose decreases with increasing cooking time, whereas the proportion of xylose increases as the cooking time increases to 3 hrs. Again in every spent liquor samples (excepting the one obtained by digestion for 1 hr), the lignosulfonate fraction amounts to 65% of the total organic material content of the liquor. Its functional group contents (excepting -COOH content) and extinction coefficient (at 280 nm) are smaller than those of lignosulfonic acid from acid sulfite pulping. On the other hand, the saccharide fraction separated is composed of oligosaccharides and some acetonesoluble organic compounds, but contains no simple sugars.