Dielectric properties (the dielectric constant (epsilon') and the dielectric loss factor (epsilon '')) and the penetration depth of raw eye of round beef Semitendinosus muscle, raw beef marinated in gravy, raw beef cooked in gravy, and gravy alone were determined as a function of the temperature (20-130 degrees C) and frequency (27-1,800 MHz). Both epsilon' and epsilon '' values increased as the temperature increased at low frequencies (27 and 40 MHz). At high frequencies (915 and 1,800 MHz), epsilon' showed a 50 % decrease while epsilon '' increased nearly three fold with increasing temperature in the range from 20 to 130 degrees C. epsilon' increased gradually while epsilon '' increased five fold when the temperature increased from 20 to 130 degrees C. Both epsilon' and epsilon '' of all samples decreased with increase in frequency. Marinating the beef in gravy dramatically increased the epsilon '' values, particularly at the lower frequencies. Power penetration depth of all samples decreased with increase temperature and frequency. These results are expected to provide useful data for modeling dielectric heating processes of marinated muscle food.