Glucoamylase (EC 3.2.1.3. from Aspergillus niger) was immobilized onto the magnetic polystyrene particles including active groups. These particles were used in a magnetically stabilized fluidized bed reactor, and performance of this reactor was investigated. Magnetically stabilized fluidized bed reactor was made of a jacketed glass column and a coaxial selenoid covering the whole column as the magnetic field source. An axial and homogeneous magnetic field was introduced to the column by using direct current. The effects of flow rate and magnetic field intensity on the particle behaviour in the column were investigated. The optimum operational conditions for magnetically stabilized fluidized bed reactor were determined and the activity performance of the immobilized glucoamylase in the reactor was researched. Higher activities were obtained at low magnetic field intensities because of no additional diffusion problems coining from particle agglomeration occured in the column when the magnetic field intensity was high. It was found that the fluid flow rate in the column must be as low as possible because higher flow rates require higher magnetic field intensities to keep the particles in the column. (C) 2000 Elsevier Science Inc. All rights reserved.