The results of measurements of the refractive index and dielectric constant of several samples of porous materials in terahertz (THz) and microwave ranges are presented in the work. Such measurements are relevant, since porous materials have a wide variation of parameters and reference data do not reflect all their diversity.The permittivity of the materials was measured in the microwave range. The cylindrical waveguide-dielectric resonator on an evanescent waveguide was used. Measurements were made by two methods at frequencies of 10 ÷ 12 GHz. In one method, the investigated material was used as the dielectric element of the resonator. In another method, the dielectric element was made of fluoroplastic and the investigated material filled the evanescent parts of the waveguide. The accuracy of measurements was compared and the advantages and disadvantages of these methods were analyzed.The measurements were carried out in the THz range by a resonance method at a frequency of 890 GHz. A gas-discharge submillimeter laser with a wavelength of 337 μm was used for this purpose. The measuring device was a quasi-optical resonator with a smooth length adjustment. One of the mirrors of the quasi-optical resonator was simultaneously the output mirror of a submillimeter laser. The test material was placed in a quasi-optical resonator. The refractive index was determined from the change in the optical length of the resonator, when the investigated material was introduced into it.The difference in the measured parameters for the different materials studied correlates with the specific gravity of the materials. Significant changes in the parameters when changing the frequency have not been detected.The results of measurements can be used in the development of various devices with THz and microwave ranges, in particular, in the design of antenna fairings, dielectric waveguides, quasioptical elements, etc.