The development of injectable microparticles for protein delivery is a major challenge. We demonstrated the possibility of entrapping human serum albumin (HSA) and thrombin (Thr) in poly(ethylene glycol) (PEG)-coated, monodisperse, biodegradable microspheres with a mean diameter of about 10 gm. In our earlier studies, diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) analysis was used to characterize the surface of PEG-coated, taxol-loaded poly(lactic acid) (PLA) microspheres. An analysis by DRIFTS revealed that PEG was incorporated well on the PLA microsphere surface. An emulsion of protein (in water) and PLA dissolved in an acetone-dichloromethane (or acetone- chloroform) mixture were poured into an aqueous solution of PEG [or poly(vinyl alcohol) (PVA)] with stirring with a high-speed homogenizer for the formation of microparticles. HSA recovery in microspheres ranged from 13 to 40%, depending on the solvent and emulsification systems used for the preparation. PLA dissolved in a dichloromethane /acetone system and albumin loaded via a PEG emulsification solution (PLA-PEG-HSA) showed maximum drug recovery (39.5%) and drug content (9.9%). Scanning electron microscopy revealed that PEG-coated microspheres had less surface micropores than PVA-based preparations. The drug-release behavior of microspheres suspended in phosphate-buffered saline exhibited a biphasic pattern. An initial burst release (30%) followed by a constant slow release for 20 days was observed for HSA and Thr from PLA-PEG microspheres. PEG-coated PLA microspheres show great potential for protein-based drug delivery.