Glucose oxidase (GOD) was covalently immobilized onto florisil (magnesium silicate) carrier via glutaraldehyde. Immobilization conditions were optimized: the amount of initial GOD per grams of carrier as 5 mg, pH as 5.5, immobilization time as 120 min and temperature as 10 degrees C. Under the optimized reaction conditions activities of free and immobilized GOD were measured. Free and immobilized GOD samples were characterized with their kinetic parameters, and thermal and storage stabilities. K(M) and V(max) values were 68.2 mM and 435 U mg GOD(-1) for free and 259 mM and 217 U mg GOD(-1) for immobilized enzymes, respectively. Operational stability of the immobilized enzyme was also determined by using a stirred batch type column reactor. Immobilized GOD was retained 40% of its initial activity after 50 reuses. Storage stabilities of the immobilized GOD samples stored in the mediums with different relative humidity in the range of 0-100% were investigated during 2 months. The highest storage stability was determined for the samples stored in the medium of 60% relative humidity. Increased relative humidity from 0% to 60% caused increased storage stability of immobilized GODs, however, further increase in relative humidity from 80% to 100% caused a significant decrease in storage stability of samples. (c) 2005 Elsevier B.V. All rights reserved.