The conditions of preparation of gentamicin sulfate microspheres with high drug loading and a particle size less than 5 mum, using a double-emulsion-solvent evaporation technique, intended for intra-ocular administration are described. The microspheres were prepared from poly methacrylate (Eudragit RS and RL) polymers cross-linked with polyvinyl alcohol. The parameters that improved the incorporation efficiency of gentamicin in the microspheres and controlled the particle size and surface morphology were investigated. Modifying the secondary aqueous phase by partially saturating it with various concentrations of either KCl or gentamicin increased the incorporation efficiency of the drug and affected the mean diameters of the microspheres. However, these characteristics were not altered when the initial drug loading was increased in the formulations. The modified gentamicin microspheres exhibited a smooth surface with an incorporation efficiency rate of 12.59% and a mean diameter of 4.06 mum. The antimicrobial efficiency of gentamicin released from the modified particles against selected Gram-positive and -negative organisms including Escherichia coli , Staphylococcus aureus and Pseudomonas aeruginosa confirmed that the entrapped gentamicin seemed to remain unaltered by the encapsulation process.