The study of the silver for sodium ions substitution kinetics is carried out using an electrochemical set-up. A silver metal anode, a reference and counter electrode are deposited as thin films on a 0.6 SiO2-0.2 B2O3-0.2 Na2O glassy electrolyte. The anode dissolution is studied by a chronoamperometric method. The generally proposed interdiffusion models assuming constant diffusion coefficients for both Ag+ and Na+ cations are not able to justify the experimental voltage time dependence. The deviation from theoretical predictions can be minimised by assuming a mixed cation effect in the glass, taking into account a concentration dependence of the Ag+ and Na+ diffusion coefficients.