Macro-, micro- and nanosized chitosan particles suitable as immobilization carriers were prepared by precipitation, emulsion cross-linking and ionic gelation methods, respectively. Effects of particle preparation parameters on particle size were investigated. Activities of beta-galactosidase covalently attached to differently sized particles have been evaluated and compared. The highest activity was shown by the biocatalyst immobilized on nanoparticles obtained by means of the ionotropic gelation method with sodium sulphate as gelation agent. beta-Galactosidase fixed on macro- and microspheres exhibited excellent storage stability in aqueous solution, with no more than 5% loss of activity after 3 weeks storage at 4 degrees C and pH 7.0.