A method for separatory determination of xylanase activity was investigated and a procedure was established as follows. Two ml of 1.0% carboxymethylxylan solution (250 μeq/g), 1 ml of 0.1M acetate buffer solution (pH 4.5), and 1 ml of enzyme solution in a 25 ml Nesler tube was incubated at 37°. After 30 min, xylose formed in the reaction mixture was determined by the Tauber -Kleiner's method (exo-xylanase activity). By using the Somogyi-Nelson's method instead of Tauber -Kleiner's method, free reducing sugar in the reaction mixture was determined (total xylanase activity). At the same time, a blank test was performed by replacing active enzyme solution with heat-inactivated enzyme solution and the amount of reducing sugar in a blank test was subtracted from that of the sample. Exo-xylanase activity subtracted from total xylanase activity was defined as endo-xylanase activity. One unit of xylanase activity was defined as the amount of enzyme which will liberated 1 mg of xylose under the above condition.