The potential of the modified magnetic nanoparticles for covalent immobilization of porcine pancreatic alpha-amylase has been investigated. The synthesis and immobilization processes were simple and fast. The co-precipitation method was used for synthesis of magnetic iron oxide (Fe3O4) nanoparticles (NPs) which were subsequently coated with silica through sol-gel reaction. The amino-functionalized NPs were prepared by treating silica-coated NPs with 3-aminopropyltriethoxysilane followed by covalent immobilization of alpha-amylase by glutaraldehyde. The optimum enzyme concentration and incubation time for immobilization reaction were 150 mg and 4 h, respectively. Upon this immobilization, the alpha-amylase retained more than 50 % of its initial specific activity. The optimum pH for maximal catalytic activity of the immobilized enzyme was 6.5 at 45 A degrees C. The kinetic studies on the immobilized enzyme and its free counterpart revealed an acceptable change of K-m and V-max. The Km values were found as 4 and 2.5 mM for free and immobilized enzymes, respectively. The V-max values for the free and immobilized enzymes were calculated as 1.75 and 1.03 mu mol mg(-1) min(-1), in order, when starch was used as the substrate. A quick separation of immobilized amylase from reaction mixture was achieved when a magnetically active support was applied. In comparison to the free enzyme, the immobilized enzyme was thermally stable and was reusable for 9 cycles while retaining 68 % of its initial activity.