Colloidal crystals have attracted considerable attentions due to their interesting structures and potential applications. Colloidal crystals are generally prepared through evaporation-induced self-assembly method from monodispersed microspheres due to its simple device and low cost. However, various defects usually appear because of weak interface bonding between spheres during the self-assembly process and shrinkage during the evaporation process. In this article polystyrene (PS) microspheres were surface modified using UV light/ozone treatments. X-ray photoelectron spectrometer (XPS) and Fourier transform infrared (FTIR) spectroscopy show that PS spheres are well surface modified with hydroxyl and carbonyl groups after UV/ozone treatment for 1800 s. The modified PS microspheres were further self-assembled into colloidal crystals. Fewer defects and better crystal quality of templates are obtained after surface modification of PS nanospheres. The reflection spectrum of colloidal crystals is also measured with higher reflectivity and sharper reflectance peek. All the results show that UV/ozone treatment of PS colloidal spheres is beneficial for improving the degree of order of colloidal crystals. This provides a simple and feasible way for the application of large area colloidal crystals. (C) 2011 Elsevier B.V. All rights reserved.