One of the most important parameters in characterization of integrated optical devices is precise determination of the effective cut-off wavelength of the fundamental and first-order modes, since this sets the exact region of single-mode operation. This paper describes an experimental set-up for determination of cut-off wavelengths of integrated optical waveguides, using the technique of spectral light transmission. Measurement results obtained with Ti:LiNbO3 channel waveguides are presented for straight waveguides, bent waveguides and polarizers.