TiO2 thin films were deposited on both bare Si and Si substrates with ZnO buffer layer (ZnO/Si) by radio frequency (rf) magnetron sputtering of TiO2 target at a substrate temperature of 500. A mixed gas of Ar and O2 was used for sputtering and O2 flow ratio was changed from 0 to 30%. X-ray diffraction patterns showed that the TiO2 thin films had only rutile structure. The weak diffraction peak from the (110) plane of rutile structure was observed for the TiO2 film formed on bare Si substrate. For the TiO2 film on ZnO/Si, the diffraction peak from the (200) rutile structure was dominant. The diffraction intensity from the rutile structure of TiO2/ZnO/Si was stronger than that of TiO2/Si. This implies that ZnO buffer layer promoted the crystallization of rutile structure.