In this work the optical and the gas sensing properties of thick TiO2 waveguide films, produced by pulsed laser deposition, were investigated by m-line spectroscopy. The films were deposited on (0 0 1) SiO2 substrates at temperature of 100 degrees C. The thickness of the films was measured to be in the range from 650 to 1900 nm and the roughness increases from 5 to 14.6 mn. High quality mode spectra, consisted of thin and bright TE and TM modes, were observed in the films with thickness up to 1200 run. All the films revealed anisotropic optical properties. Gas sensitivity of the films to CO2 was examined at room temperature on the basis of the variations of the refractive index. CO2 concentration of 3 x 10(4) ppm was detected, which corresponds to a refractive index variation of about 1 X 10(-4). The crystal structure and the optical transmittance of the films were also presented and discussed. (C) 2007 Elsevier B.V. All rights reserved.