Double-walled microspheres trapping gentamicin sulphate were prepared from poly(L-lactic acid) (PLLA) and poly(L-lactic-co-glycolic acid) (PLGA) as a delivery system for highly hydrophilic antibiotics. The surface and cross-section morphology of the microspheres were characterized by SEM and FTIR. The diameters of the microspheres were ranging from about 50 mu m to 700 mu m. A low initial burst was achieved. The encapsulation efficiency was more than 70% and the cumulative drug release was about 40% for 30 days. The results indicated that the double-walled microspheres were able to achieve higher encapsulation efficiency and lower initial burst for highly water-soluble drugs. (c) 2008 Elsevier B. V. All rights reserved.