This article describes the preparation and characterization of BSA and bFGF-loaded PLGA microspheres and assesses the effect of entrapment procedure and in vitro release conditions. In the experiments, changing the PVA concentration from 3 to 5% (w/v) in the pre-emulsion innerphase led to a change in particle size and encapsulation efficiency of BSA-loaded and bFGF-loaded PLGA microspheres from 1 to 0.7 mu m and from 73 to 65%, respectively. The in vitro release of the bFGF from PLGA microspheres was much lower than BSA-loaded PLGA microspheres. For all of the formulations, BSA and bFGF retained integrity after the microencapsulation process as evaluated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). Besides, the cell proliferation-stimulating activity of bFGF was evaluated by using BALB/c 3T3 cells and it was shown that the bioactivity of bFGF was increased by adding heparin to the release medium.