Dielectric relaxation measurements of formamide (FMD)–$N,N$- dimethylaminoethanol (DMAE) solvent mixtures have been carried out over the entire concentration range using time domain reflectometry technique at 25, 35 and 45° C in thefrequency range of 10 MHz to 20 GHz. The mixtures exhibit a principle dispersion of the Davidson–Cole relaxation type at microwave frequencies. Bilinear calibration method is used to obtain complex permittivity $\epsilon^{∗}(\omega)$ from complex reflection coefficient $\rho^{∗} (\omega)$ over the frequency range of 10 MHz to 10 GHz. The excess permittivity ($\epsilon^{E}$), excessinverse relaxation time $(1/\tau)^{E}$, Kirkwood correlation factor ($g^{eff}$), activation energy and Bruggeman factor ($f_{B}$) are also calculated to study the solute–solvent interaction.