beta-Galactosidase enzyme, from Aspergillus oryzae, was covalently immobilized onto amino-functionalized PVC microspheres after activation with gultaraldehyde. PVC microspheres were functionalized by introducing terminal amine groups via amination process with ethylene diamine (EDA). Furthermore, verifications of amination process were obtained using TGA, FT-IR, and SEM analysis. Different factors affecting the amination process were investigated and their impact on the activity and the retention of immobilized enzyme's activity was monitored. Concentration of ethylene diamine, amination temperature, and time were found for a determined effect. Reaction with EDA (0.025%) at 30 degrees C for 40 minutes was found for optimum conditions. Variation of PVC : EDA mass ratio over 1 : 1 was found with neglectable effect. Thermal stability of immobilized enzyme was recognized where the immobilized form kept 80% of its original activity compared with 20% for the free form. Denaturation tolerance against pH was observed where immobilized form kept 60% of its original activity after 300 minutes incubation at pH 7.0 in the absence of substrate while the free form kept only 15% of its activity under the same conditions. Moreover, immobilized form show storage stabilities where immobilized form kept 40% of its original activity after four weeks while the free form kept only 25% of its initial activity. Under optimum conditions for enzyme immobilization, 1 kg of immobilized enzyme retains 87% of its native activity and has 11,000 activity units. (c) 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012