beta-galactosidase was immobilized into pHEMA membranes with the highest specific activity yield of 9.5%. The specific activity of the entrapped enzyme was found to be decreased as the enzyme loading increased in pHEMA membranes. The optimum pH and temperature for maximum activity of the immobilized beta-galactosidase was found to be at pH 7.5 and 50 degrees C, respectively, and were the same as native enzyme. K-m and V-max values for the free enzyme were found to be 0.256 mM and 26.6 mu mole/min/mg, respectively. K-m value of immobilized beta-galactosidase was found to be increased about 3 folds upon immobilization. Operational, thermal and storage stability of beta-galactosidase were found to increase with immobilization. Immobilized enzyme preparation was reused in 15 cycles without significant loss in activity.