Mercury oxidation in presence of bromide and chloride in MeCN solutions has been studied by direct and reverse chronopotentiometry under a wide range of experimental conditions. The reactions follow the same scheme already postulated for iodide solutions with mercury halide complex formation of the type HgX n (2− n ) . The instability constants for the HgX 4 2− complexes are in the sequence Cl − > Br − >I − . Mercury dissolution is facilitated by halide adsorption at the interface. The adsorption sequence is I − >Br − >Cl − and adsorption is enhanced by Et 4 N + . The possibility of ion pairing between the complexing agent and the cation of the supporting electrolyte is analysed to explain the different behavior observed with chloride solutions in presence of Li + ions.