A method using standard waveguide components is described for accurate measurements of complex dielectric permittivity of low, medium, and high loss liquids up to 150 GHz. Measurements on cyclohexane, carbon tetrachloride, chloroform, and 1,1,1‐trichloroethane are reported. The data of chloroform are compared with results from different authors, confirming an additional absorption above 40 GHz. The method is also suitable for determining the level of the continuous spectra obtainable by far infrared Fourier transform spectroscopy.