In this work, a double frequency Q-switching Nd:YAG laser beam (λ=532nm, laser fluence 1.2 J/cm2 ,repetition rate 10 Hz and the pulse duration 7ns) has been used, to deposit TiO2 thin films pure on glass and Si (111) substrates .The structure properties of pure TiO2 were investigated by means of x-ray diffraction. As a result, it has been found that film structure and properties strongly depended on substrate temperature. X-ray diffraction (XRD) showed that at substrate temperatures higher than 300 °C the structure of the deposited thin films changed from amorphous to crystalline corresponding to the tetragonal TiO2 anatase phase.The surface morphology of the deposits materials have been studied using scanning electron (SEM) and atomic force microscopes (AFM). The grain size of the nanoparticles observed at the surface depended on the substrate temperature, where 500°C was the best temperature and partial pressure of oxygen 5×10-1 mbar was the best pressure during the growth process. RMS roughness increased with increasing substrate temperature (Ts) which are (11.2nm) for thin films deposited at (500)ºC.UV-VIS transmittance measurements have shown that our films are highly transparent in the visible wavelength region, with an average transmittance of ~90% which makes them suitable for sensor applications . The optical band gap of the films has been found to be 3.2 eV for indirect transition and 3.6 eV for direct transition at 400˚C.The sensitivity toward CO gas has been measured under 50 ppm.