Aqueous two-phase partitioning system (ATPS) was used to extract and purify catalase from Bacillus pumilus. The system parameters for effective purification of catalase were optimized. The best catalase recovery (123%) with a 4.6-fold purification was obtained in the bottom phase of ATPS including the mixture of 15% (w/w) PEG4000, 10% (w/w) Na2SO4 and 3% (w/w) NaCl at pH 5.0. The purified enzyme was characterized regarding its activity and stability. The highest enzyme activity was observed at pH 7.0 and 37 degrees C on hydrogen peroxide. The enzyme was quite stable at temperatures between 30 and 55 degrees C and a pH range of 7.0-9.0. The K-m and V-max values were determined from Lineweaver-Burk plot as 11 mM and 1667 mu mole ml(-1) min(-1), respectively. Overall, it can be said that ATPS is a rapid, reasonable, straightforward and cost-effective process for catalase purification in comparison to the chromatographic methods.