Impedance spectroscopy (IS) was used for the determination of the static dielectric permittivity and the electric conductivity of N-methylacetamide (NMA) + N,N-dimethylacetamide (DMA) mixtures over the whole concentration range and over the temperature range of 303.15 K to 393.15 K. The static permittivity values obtained with IS for both neat compounds at different temperatures are in a very good agreement with those measured with the classical dielectric methods. In NMA + DMA mixtures, the permittivity deviations (Delta epsilon) from the concentration additive rule are strongly negative, and the Delta epsilon dependence on the mole fraction of NMA was fitted to the Redlich-Kister equation.