The stress relaxation during the interruption of cobalt thin film growth by electrodeposition was monitored by the cantilever bending technique. The surface morphological evolution of cobalt thin films during stress relaxation was characterized by atomic force microscopy. Unlike the stress relaxation of a perfect cobalt film, the relaxation of cobalt film with surface imperfections displayed irreversible character and was suggested to be the result of cobalt dissolution in electrolytes. Additionally, the irreversible stress relaxation was accompanied by mass loss and open circuit potential change, supporting the dissolution mechanism. Scaling analysis of the morphology evolution indicated that the local stress is one of the primary driving forces for the dissolution. Additives containing Cl⁻ silenced the stress relaxation by improving the smoothness of the film surface.