This work was aimed at studying enzyme prolidase stability and its interactions with the reagents and the process conditions involved in preparation, by an emulsification process, of prolidase loaded poly(lactide-co-glycolide) (PLGA) microparticulate systems. Enzyme stability was tested with respect to contact with methylene chloride, ethyl acetate, PLGA polymers, and several agents used as emulsifiers such as polyvinyl alcohol (PVA), polyvinyl pyrolidone (PVP), carboxymethyl cellulose (CMC) and sodium oleate (NaOl). Enzyme stability to temperature and mechanical stirring was also evaluated. Prolidase-loaded PLGA microspheres were prepared and evaluated in terms of protein activity. The results obtained showed that the prolidase-loaded PLGA microspheres can be prepared only upon enzyme stabilization by addition of both BSA and MnCl(2) into its TRIS solution. Methylene chloride was the suitable organic solvent to be used in the double emulsion process, together with PVA as dispersing agent in the outer aqueous phase. Low temperatures during the emulsification step and very short process times are recommended, in order to maintain enzyme activity at its maximum. In these conditions spherical microspheres were obtained, releasing active prolidase for up to 15 days.