Abstract：Colloidal silica photonic crystals were prepared by using ethanol as medium. Nanospheres with a mean diameter of 238 nm and standard deviation 5.7% were obtained under strictly controlled conditions by using the improved Stober method. In this method, ethanol was proved a better medium than water and the prepared photonic crystals had fewer defects. The diffraction to incident infrared light obeyed the Bragg equation. The formation mechanism and defect formation of colloidal photonic crystals were also discussed.