ZnO/PMMA inorganic/organic composite microspheres were synthesized with a yield of 83 wt% via soap less emulsion polymerization. The hydrophobic ZnO nanoparticles were modified by oleic acid (OA), which could improve the compatibility between ZnO nanoparticles and methyl methacrylate (MMA) monomer in emulsion system. The existence of ZnO was indicated by the XRD characteristic peaks of the composite microshperes. The TEM micrographs showed that the morphology of the composite microspheres was uniform and ZnO nanoparticles could be encapsulated in the PMMA polymer microspheres. When the ZnO nanoparticles participated in the polymerization process, the surface morphology of composites microspheres changed from smooth to grooved which was characterized by FESEM. In addition, the fluorescence property of the ZnO/PMMA composites became stronger with the increasing amount of ZnO nanoparticles and the fluorescence absorption was stronger than that of pure ZnO.