The electric double layer structure at the electrochemically polished Cd(0001), Cd(10 (1) over bar 0), Cd(11 (2) over bar 0), Cd(10 (1) over bar 1) and Cd(11 (2) over bar 1), and chemically treated Cd(0001), Cd(10 (1) over bar 0) and Cd(11 (2) over bar 0) electrodes in aqueous surface-inactive electrolyte solutions was studied using cyclic voltammetry, impedance and chronocoulometry. The limits of ideal polarizability, potentials of zero charge and capacity of the inner layer were established. Like those for the respective single crystal planes of Zn, the value of the zero charge potential decreases and the inner layer capacity increases if the superficial density of atoms decreases. The capacity of the metal phase was established using the various theoretical approximations. The effective thickness of the thin metal layer increases in the sequence of planes Cd(11 (2) over bar 0) < Cd(10 (1) over bar 0) < Cd(0001) as the surface density of atoms increases.