This paper describes Rh electrodeposition on Pt electrodes in HClO4 solutions. Using cyclic voltammetry (CV), coupled with electrochemical quartz crystal microbalance (EQCM) studies, we determined the main characteristics related to oxide formation on rhodium deposited on platinum. During the deposition, the results demonstrated that Rho ad-atoms are stable on Pt in the potential range investigated at different saturation coverages. Data obtained using EQCM and CV show that the number of electrons transferred in the oxidation of Rh-ads on Pt is 3 and a Rh(OH)(3) species was proposed as the adsorbed product. At potentials higher than 1.0 V, Rh(OH)(3) is oxidized to RhO(OH)(3). This species is reduced to Rh(OH)3 and then to Rho during the negative potential sweep. (C) 2004 Elsevier B.V. All rights reserved.