Abstract The electrochemical stability of polycrystalline rhodium and rhodium nanoparticles is quantitatively investigated in non-complexing sulfate electrolyte under potential cycling conditions. In situ measurements of the active surface area are complemented by discrete elemental analysis of the electrolyte solution. Rhodium electrodes are not stable and dissolve upon potential excursions into the oxide region above approximately +0.5 V RHE ; the higher the positive potential limit, the higher the mass loss rate per cycle. Interestingly, the normalized catalyst mass loss is independent of the initial catalyst loading under identical conditions. The dissolution of Rh and the concomitant structural changes have to be considered in any further electrocatalytic study of this kind of electrodes.