Interfacial stress changes at electroactive self-assembled monolayers have been investigated by monitoring C the potential-induced deflection of Au-coated microcantilevers modified with 12-ferrocenyl-1-dodecanethiol in aqueous perchloric acid solution. Oxidation of the surface-bound ferrocene generates a compressive surface stress which results in the cantilever bending away from the film-coated An surface. The origin of the redox-induced stress change that occurs at these close-packed monomolecular films is discussed.