The open-ended coaxial technology was used to measure microwave dielectric properties and quality indices of heated mixed edible oil at 120～240℃ for 3～15h over the frequency range from 200 to 4500MHz. Results showed that, without high-temperature heating, the relative dielectric constant and loss factor of the oil would change with frequency, but kept constant generally when the oil was heated. The dielectric constant of heated oil was lower and the loss factor was higher than that of unheated oil. The high-temperature and heating time had small effect on permittivities. When the temperature was higher than 180℃, the acid value increased with heating time, but the time had obvious effect to peroxide value when the temperature was 120℃.