In this work, a series of porous terpolymers with degrees of crosslinking at 30-65% were synthesized by suspension polymerization. Fe3O4 nanoparticles were used to modify the porous terpolymer with degree of crosslinking at 30%. The resulting terpolymers with mean pore size of 10-30 nm were used as supports for immobilization of cellulases through covalent bondings. The Fourier transform infrared spectroscopy and thermal gravity analysis measurements demonstrated that cellulases were immobilized onto the porous terpolymers. The effects of pH and temperature on enzyme activity were investigated in acetate buffer medium by hydrolysis of sodium carboxymethyl celluloses. The reusability of immobilized cellulases was also investigated. The result showed that immobilized cellulases exhibited higher residual activities and enzyme activities than free cellulases in wide ranges of pH and temperature. We also found that the reusability of cellulases immobilized on terpolymers with magnetism was better than that of cellulases immobilized on terpolymers without magnetism. POLYM. ENG. SCI., 55:1039-1045, 2015. (c) 2014 Society of Plastics Engineers