The electrochemical behavior of the Co-Sb system on Au substrate during cyclic voltammetry and potentiostatic deposition was investigated. Electrochemical behavior of Co and Sb was studied and compared to the Co-Sb system. At a negative potential (-0.9 V vs. Ag/AgCl) the electrochemical behavior of this binary system was similar to that of individual Co and Sb combined. For more negative vertex potentials (e.g., -1.2 V vs. Ag/AgCl), results from cyclic voltammetry have shown the presence of a new compound different from Co and Sb which could only be detected at slow sweep rate. The deposition performed at constant potentials between -1.0 and -1.2 V have resulted in films that were made of CoSb3 and Sb as indicated by XRD. Surface film studied by SEM and EDS has shown morphological and compositional non-uniformities caused by hydrogen evolution.