In this paper, the authors report new abnormal photoluminescence results of TiO2 nanocrystal particles and nanotube arrays. Photoluminescence spectra were recorded for TiO2 nanocrystal particles and nanotube arrays that were synthesized by a wet chemical route and the electrochemical anodization, respectively. It was found that the TiO2 nanocrystal with small size of 5-8 nm no emitted when excited by a laser beam of 325 nm, in contrary it emitted when excited by laser beam of 442 nm. The TiO2 nanotube arrays exhibit a similar emission behavior. The nanotube arrays weakly emitted when excited by a laser beam of 325 nm and more strongly emitted when excited by a laser beam of 442 nm. The obtained results have been explained by a two-step exciting model and supposed to be ,related with the size effect of nanocrystal and it is an experimental evidence to believe that the TiO2 nanoparticles and'nanotube arrays are applicable for photo-catalysis under sun light.