Dielectric properties of butter with and without salt (moisture content 17-19%) were measured over the MW frequency range covering 500-3000 MHz. The effect of temperature on dielectric properties of butter was studied at 10 degrees interval between 30 and 80 degrees C. Results indicated that dielectric spectra of unsalted butter differed significantly (P < 0.05) from the salted one as function of temperature. The dielectric constant (epsilon') of unsalted butter was independent of frequency whereas the loss factor (epsilon") decreased with an increase in frequency. Both epsilon' and epsilon" of unsalted butter decreased as the temperature increased. Dielectric parameters of salted butter gradually decreased with increasing frequency but increased with temperature. The dielectric properties of both salted and unsalted butter were adequately described by a second order polynomial equation. The increase in ionic conductance as a result of salt appears to be the principal reason for the differences in electrical properties of salted butter. Butter converted to butter oil (at elevated temperatures) exhibited significant drop in dielectric parameters possibly due to the lack of water. Power penetration depth of butter decreased with temperature, frequency, and salt content. (C) 2007 Elsevier Ltd. All rights reserved.