In this paper, a new corrosion sensor based on a quartz crystal microbalance is presented. A 50 mum thick disk of solid metal is glued directly on the surface of a 2 MHz AT-cut quartz crystal. An electronic oscillator designed for highly damped quartz resonators allows the resonance frequency of the quartz-glue sample system to be followed. Simultaneous electrochemical measurements are possible as the metal sample can be polarized. The mass sensitivity of this electrochemical quartz crystal microbalance was determined by carrying out a copper electrodeposition directly on the sample surface. The potentiostatic dissolution of 304 stainless steel in 1 M HCl is discussed in this paper. The mass loss during potentiostatic dissolution was measured by the frequency shift of the microbalance sensor and compared to the mass loss calculated from Faraday's law. A very good agreement was found as both results had a relative difference lower than 5%.