Redox reaction mechanism in absence and presence of Valporic Acid (VaA) was studied in cyclic voltammetry, we used a new silver electrode made from pure Silver piece jointed to copper wire and isolated by heat shrink polymer to insure Complete isolation, during measurements. The Silver electrode was polished with Al 2 O 3 in woolen piece, washed and used for the cyclic voltammetric Study. The stability constants and Gibbs free energies of complex reactions between HgCl 2 and Valproic acid (VaA) in 0.01 M KNO 3 at 22˚C were evaluated and their results were discussed.