Abstract: OBJECTIVE To prepare bovine serum albumin (BSA) cationic microspheres for oral administration, and investigate the influence of natural cationic polysaccharide chitosan (CHS) on size, eletrokinetic potential, encapsulation efficiency, loading capacity and in vitro release profile of BSA microspheres. METHODS PLGA/CHS microspheres were prepared by W/O/W emulsion-solvent evaporation method. Orthogonal design method was used to determine the optimal formulation. A simple and precise method for the determination of the protein content was established. In vitro evaluation of PLGA/CHS microspheres was carried out. RESULTS The optimal formulation was as follows: 150 mg·mL-1 of BSA, 8% PLGA solution, 80 mL of external aqueous phase, 0.2% chitosan solution. The PLGA/CHS microspheres were spherical. The average particle size of the microspheres was (6.9 ± 5.5)μm, the eletrokinetic potential (ζ potential) was (10.0±0.6)mV. The drug loading capacity and encapsulation efficiency were (9.3 ± 0.2)% and (75.4 ± 4.6)%, respectively. In vitro release studies show that chitosan can decrease the burst release and delay the release of drugs in both simulated gastric fluid and simulated intestinal fluid. CONCLUSION Compared with PLGA microspheres, PLGA/CHS cationic microspheres has higher encapsulation efficiency and loading capacity, and slow-release, while reducing burst release.