The trypsin was successfully immobilized on the surface of magnetic carboxymethyl chitosan( Fe3O4( PEG + CM-CTS)) nanoparticles by electrostatic interaction. The effects of the medium p H,the concentration of trypsin and the immobilization time on trypsin loading and relative activity onto the magnetic nanoparticles were discussed. The results show that the adsorption equilibrium of trypsin onto the Fe3O4( PEG + CM-CTS) magnetic nanoparticles well fits Langmuir model,and the maximum trypsin loading is 117. ...