One of the most important parameters in the characterization of integrated optical waveguides is the precise determination of the effective cut-off wavelength of the fundamental and the first order mode, since it sets the exact region of single-mode operation. This paper describes an experimental set-up for the measurement of the cut-off wavelengths of integrated optical waveguides, using the technique of spectral light transmission. Measurement results obtained with Ti:LiNbO3 channel waveguides are presented. The effect of different geometrical parameters and fabrication conditions on the cut-off wavelengths of the channel waveguides for both TE and TM mode excitation will be discussed.