The purpose of this article is to explore the methods preparing biodegradable microspheres delivery system of vaccines by oral targeting administration.A series of polymers of DL lactide and polyethylene glycol(PEG) with different contents of PEG were synthesized and the microspheres containing human serum albumin(HSA) were prepared by a solvent evaporation method using a W/O/W emulsion.The scanning electron micrograph of microspheres showed a smooth and spheric surface.The size of microspheres could be controlled between 0.5～10μm

which is essential for microspheres to reach the target sites.The amount of protein in microspheres was 2.5% determined by CBB method and the entrapemnt ratio achieved approximately 80%.It was concluded that the properties of polymers

stabilizer system and solvent in oil phase and great effect on the formation of microspheres

particle size and the protein entrapment ratio.In vitro studies indicated that protein-carrying microspheres of PLA had a larger burst-effect than that of PELA-10.