Near field characterization of optical waveguides is extremely important in monomode waveguides production. This work has use a measurement system based on the near field measurement, for characterizing the modal contents of waveguides. In order to verify the modal characteristics of two GaAS/AlGaAs waveguides, with different structures, near fiels measurements were made. Important parameters, such as the alignment and the focal adjustment of the aoptical systems, were also analyzed. Using the results from the measurements, it was calculated the spot size of the waveguides in the horizontal and vertical directions, verifying the coupling efficiency with monomode fibers. A calibrated monomode fiber was measured to analyze the system precision. On using this measurement as a reference parameter a high precision was observed