Continuous wave CO2 laser was irradiated on SiO2/TiO2 composite nanoparticles generating in a flame to in-situ control the crystalline phase. The laser irradiation was not only shown to transform originally amorphous composite nanoparticles into the crystalline ones, but also to control the crystallite size of TiO2 embedded in SiO2 nanoparticles by altering the irradiating laser power. X-ray diffraction analysis and transmission electron microscope analysis confirmed that the size of TiO2 anatase crystallites in silica nanoparticle increased with increasing the irradiation laser power. It was shown that the corresponding absorption edge of SiO2/TiO2 composite nanoparticles could be controlled by changing the crystallite size of TiO2 inside SiO2 nanoparticles. (C) 2012 Elsevier B.V. All rights reserved.