Abstract: Poly-DL-lactide-b-polyethylene glycol (PELA) block copolymerswere synthesized by ring- opening polymerization of lactide with polyethylene glyco.l PELA microspheres containing human serum albumin (HSA) were elaborated by the solvent extraction method based on the formation of doubleW1/O/W2emulsion. The microspheres with an idealmean diameter of 1. 36μm and a size distribution ranging from 0. 5 to 5μm were smooth and spherica.l The effects of concentration of alginate/CaCl2added in the internal water phase on the encapsulation efficiency ofHSA and the characteristics of the microspheres were investigated, and the content of protein in the microspheres was testedwith the CBB (Coomassie brilliant blue) method. The results show that the encapsulation efficiency is improved obviouslywhen the concentration of added alginate/CaCl2is 3. 0% (W /W) in the internalwater phase.