The efficiency of xylanase of Bacillus brevis BISR-062 as a prebleaching agent was evaluated on three nonwoody pulps at two different pH values (7.0 and 8.5). Crude xylanase was found to have an optimum temperature and pH of 65-70 degrees C and 7.0, respectively. The stability of the enzyme was determined at two pH values (7.0 and 8.0), and it lost approx 50% of its activity at both values within 2 h at 50 degrees C. However, the enzyme was found to be effective as a prebleaching agent only with rice straw pulp. A maximum brightness gain of 6 points was obtained with this pulp at pH 7.0. The strength properties of the rice straw pulp at pH 7.0 also improved as the result of enzyme treatment.