The aim of this study is to prepare cationic biodegradable dextran microspheres loaded with  tetanus toxoid (TT) and to investigate the mechanism of protein loading.  Positively charged microspheres were prepared by polymerization of hydroxylethyl methacrylate derivatized dextran (dex-HEMA) and dimethyl   aminoethyl methacrylate (DMAEMA) in an aqueous two-phase system.  The loading of the microspheres with TT was based on electrostatic attraction.  The net positive surface charge increased with increasing amounts of DMAEMA.  Confocal images showed fluorescein isothiocyanate labeled bovine serum albumin (FITC-BSA) could penetrate into cationic dextran microspheres but not natural dextran microspheres.  TT loading efficiency by post-loading was higher compared with by pre-loading.  Even though TT is incorporated in the hydrogel network based on electrostatic interaction, still a controlled release can be achieved by varying the initial network density of the microspheres.