This study applied the measurement of dielectric properties and reflection coefficient by using Agilent E8362B slim probe. Slim probe and open-ended coaxial sensor are implemented to measure the dielectric properties and reflection coefficient of the cooking oil samples. The vegetable oils were purchased from the local market and were heated in the oven. Five types of cooking oil are corn oil, olive oil, palm oil; sunflower oil and walnut oil were measured at the temperature of 60°C, 80°C and 100°C for the frequency range of 0.2 GHz to 20GHz. As the oil, undergoes thermal degradation during heating, the chemical chain of oil will be altered and resulting in physical and internal properties change. Dielectric properties are part of physical-chemical properties of cooking oil that can be measured to inspect the oil quality. According to the dielectric properties and reflection coefficient measurement, there are different noticeable signal pattern which indicates the used and fresh cooking oil and the effect of heating period
