Abstract: This paper presents a novel microstrip patch antenna sensor for detecting the quality of edible oil. The relative dielectric constant and the quality of edible oil will be changed after the edible oil is heated at high temperature, so the quality of edible oil can be detected by measuring its relative dielectric constant. The sensor is used to determine the edible oil with different dielectric constants by measuring the resonance shift of the resonance frequency of the input reflection coefficient, which operates around two central frequency points, 1. 43 GHz and 2. 68 GHz. The sensor is designed based on a resonant approach to provide the best sensing accuracy and is implemented using a substrate integrated waveguide structure combined with a pentagonal slit antenna operating at 3. 2 GHz. The device can detect greasy liquids with different dielectric constants, and the measured relative dielectric constant is the true part of the complex dielectric constant, ranging from 2. 41 to 2. 83. Thus, the proposed patch microfluidic sensor can be well used for the determination of edible oil quality and has a great potential for applications.