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We developed a method, by combining electrochemical and electrokinetic streaming current techniques to study ion distribution and ionic conductivity in the diffuse part of electrochemical double layer (EDL) of a metal-electrolyte interface, when potential is applied on the metal by a potentiostat. We applied this method to an electrochemically clean polycrystalline gold (poly Au)-electrolyte interface and measured zeta potential for various applied potentials, pH, and concentration of the electrolyte. Specific adsorption of chloride ions on poly Au was studied by comparing measurements of zeta potential in KCl and KClO₄electrolytes. In absence of specific adsorption, zeta potential was found to increase linearly with applied potential, having slope of 0.04–0.06. When Cl⁻adsorption occurs, zeta potential changes the sign from positive to negative value at ∼750 mV vs Ag/AgCl applied potential. Complementary cyclic voltammetry and X-ray photoelectron spectroscopy studies were conducted to determine a degree of chloride ion adsorption on a poly Au. A correlation was observed between the applied potential at which zeta potential is zero and potential of zero charge for poly Au. Ion-distribution and ionic conductivity in the diffuse layer were calculated from the measured zeta potential data using nonlinear Poisson-Boltzmann distribution.