Dielectric properties of highly scattering dyed corn meal have been studied in broadband microwave and millimeter-wave frequency ranges from 3.95 to 12.4 GHz and from 34 to 120 GHz. Complex dielectric permittivity has been obtained using a free-space quasi-optical spectroscopy technique and a standard waveguide transmission/reflection (T/R) calibration method. The broadband transmittance and reflectance spectra have been recorded to yield the refractive and absorption index and calculate the real and imaginary parts of dielectric permittivity. The density dependence of complex permittivity of highly scattering dyed corn meal is presented. Different scattering mechanisms and the scattering model for a corn meal material have been discussed. Detailed analysis of measurement uncertainties, including instrumentation errors, to manifest the accuracy of both techniques, has also been performed.