Composite microspheres have been prepared from bioactive ceramic such as coralline hydroxyapatite [Ca10(PO4)6(OH)2] granules, a biodegradable polymer, chitosan and an antibiotic, gentamicin. In our earlier work, we have shown a simple method of converting the calcium carbonate skeleton of the Indian corals into hydroxyapatite granules. The composite microspheres containing coralline hydroxyapatite and chitosan were prepared by dispersion polymerization technique and the gentamicin was incorporated by absorption method. The crystal structure of the composite microspheres was analyzed using X-ray powder diffractometer. The Fourier transformed infrared spectra clearly indicated the presence of amide and hydroxyl groups in the composite microspheres. Scanning electron micrographs and optical micrographs shows that the composite microspheres are spherical in shape and porous in nature. The particle size of composite microspheres was analyzed and the average size was found to be 18microns. The thermal behavior of composite microspheres was studied using thermogravimetric analysis and differential scanning calorimetric analysis. The cumulative in-vitro release profile of gentamicin from composite microspheres showed near zero order patterns. © 2002 Elsevier Science Ltd. All rights reserved.