An experimental study of the characteristics of a rectangular waveguide has been conducted. A measuring device for the experimental study of the electromagnetic field of microwave waveguides has been developed. The dispersion and attenuation in the microwave path of a rectangular waveguide have been measured. A measuring device was developed for the experimental study of the electromagnetic field of microwave rectangular and circular waveguides. The electric and magnetic fields of the rectangular waveguide operating in the frequency range of 4,9–7,05 GHz for E-type and H-type waves and the electric and magnetic fields of the circular waveguide operating at the frequency of 9 GHz for E-type and H-type waves on the developed device the dependence of the intensity values obtained from the experiment on the length of its cross section was established. The field intensities, which are the main parameters of the electromagnetic field of microwave rectangular and circular waveguides in a nonlinear environment, were experimentally measured, the relative errors between the theoretical and experimental results were evaluated and determined to be up to 4%. Parameters such as limit power, output power, extinction coefficient, standing wave coefficient, reflection coefficient, specific quality, phase of the reflection coefficient, and characteristic resistance of the rectangular waveguide are determined experimentally. The relative errors between the theoretical and experimental results for these parameters were determined to be up to 1%. This proves the adequacy of the obtained results.