A facile method for the preparation of single Quantum Dots (QDs) in silica spheres with tunable size and optical property has been developed. A time interval addition of silica precursor method has been used to increase the size of the silica shell and in parallel tuning the photoluminescence property. The resulting CdSe/ZnS/SiO2 nanocomposites were characterized by transmission electron microscopy, photoluminescence spectroscopy and zeta-potential measurements. Since for different applications of silica coated core-shell nanoparticles, control over the thickness of the shell in parallel with tuning on the optical property of the final product required, these study could pave the way for the application of this nanocomposites in different fields like photonic crystals, biolabeling, etc. (C) 2010 Elsevier Inc. All rights reserved.