A novel synthetic methodology has been developed for preparing monodispersecolloidal silica-cadmium sulfide nanocomposite spheres in the 50 – 300 nmsize regime. This methodology uses water-in-oil microemulsions as thereaction medium. Monosize silica colloids are first produced by thecontrolled hydrolysis of tetraethyl orthosilicate in the micro waterdroplets of the microemulsion. Cadmium sulfide quantum dots are incorporatedinto the silica colloids during synthesis by the introductions of Cd2+ and S2- microemulsions. Various morphologiesof the nanocomposite are fabricated by controlling the heterogeneouscoagulation of CdS and SiO2. Unique high surface area silicaparticles can be prepared when nitric acid etches out the CdS and leavesbehind topologically defined voids. The CdS nanocomposites are new materialsuseful for non-linear optics, while the high surface area silica particlesshould have novel applications in areas such as catalysis.