TiO2 thin films were deposited by metal-organic chemical vapor deposition (MOCVD) method using titanium tetraisopropoxide(TTIP). A drastic change in structural aspect and its property occurred when the deposition temperature increased above 400°C. Deposition kinetics was proved to transit from reaction controlled regime into diffusion controlled regime above about 400°C in Arrehnius plot. In X-ray diffraction (XRD)and infrared reflectance spectra, it was observed that the crystallinity was decreased significantly around 400°C. The surface microstructure has changed explicitly from dense structure with larger grains to porous one with smaller grains observed by scanning electron microscopy and transmission electron microscopy. Electrical resistance of the films jumped by 2 orders of magnitude, which is measured by the 4-point probe method. The refractive index calculated by Swanepoel's method has decreased from 2.45 to 2.28 at 630nm. The porous microstructure of films deposited at above 400°C was thought to be responsible for the significant decrease in electrical conductivity and refractive index of the films.