For the first time the chloride ion concentration in electrolyte is measured using a Kelvin probe. A silver-silver chloride (Ag/AgCl) electrode, which is a chloride ion selective electrode, is used as a sample plate in the electrolyte and the Kelvin probe is used as a reference plate that is vibrating above the electrolyte. The open-circuit potential (OCP) of the Ag/AgCl electrode is a function of the Cl- concentration. The contact potential difference (CPD), measured by the Kelvin probe, gives the OCP of the Ag/AgCl electrode. The measurement does not require any contact between the reference plate and the electrolyte. This approach opens the possibilities for using a Kelvin probe as a contactless reference electrode in electrochemical measurements, such as potentiometry.