Monodisperse SiO2/TiO2 core-shell spheres have been prepared with conventional sol-gel method. The thickness of titania coatings on SiO2 spheres was 30 nm, corresponding to 56.48 wt % titania loading and 1.66 effective refractive index of the composite particles. The relative standard deviation of composite spheres diameters distribution is 3.79%. The composite spheres were assembled, by gravity sedimentation, into three-dimensionally ordered colloidal crystals, which showed photonic band gap determined by UV-vis transmission spectrum.