The invention relates to a device for measuring the quality and/or degradation of a fluid, especially an oil, comprising a sensor consisting of at least one pair of electrodes which are distanced from each other. Said sensor is immersed in the fluid which is to be measured. The electrodes and the fluid form a capacitive element whose capacity varies according to the dielectric constant of the fluid. The sensor can provide an electric output signal representing said dielectric constant. The inventive device also comprises processing means which receive the output signal and which can determine the degree of quality and/or degradation of the fluid on the basis of said output signal. The invention is characterized in that the electrodes extend substantially on the same plane and in that the fluid surrounds the two surfaces of the electrodes on both sides of said plane.