In the present study, novel magnetic beads were prepared from glycidylmethacrylate and methylmethacrylate via suspension polymerization in the presence of a cross-linker (i.e. ethylenedimethylmethacrylate). The magnetic poly(GMA–MMA) beads were characterized with scanning electron microscope, FT-IR and ESR spectrophotometers. The reactive character of the epoxy groups allowed the attachment of the amino groups. The aminated magnetic beads were used for the covalent immobilization of β-galactosidase via glutaric dialdehyde activation. The maximum amount of immobilized β-galactosidase on the magnetic poly(GMA–MMA) beads was 9.87 mg/g support. The values of Michaelis constants Km for immobilized β-galactosidase was significant larger, indicating decreased affinity by the enzyme for its substrate, whereas Vmax values were smaller for the immobilized β-galactosidase. However, the β-galactosidase immobilized on the magnetic poly(GMA–MMA) beads resulted in an increase in enzyme stability with time. Optimum operational temperature for immobilized enzyme was 5 °C higher than that of the free enzyme and was significantly broader. Finally, a bed reactor with β-galactosidase immobilized was used for hydrolysis of lactose. The enzyme reactor operated continuously at 35 °C for 60 h and the immobilized enzyme lost about 12% of its initial activity after this period.