A double indicator electrode-containing cell of both chlorpromazinium (Cpn(+)) and chloride (Cl-) selective electrodes has been prepared. The cell exhibits a super - Nernstian value of approximately 96 mV/pCpn and a working pH range of 3.8-7.8. The cell also exhibits good selectivity of chlorpromazinium chloride (CpnCl) with respect to a large number of inorganic salt's. The potentiometric study and the X-ray photoelectron spectroscopy suggest a working mechanism of the double indicator-electrodes that can be explained by the adsorption of Cpn(+) on the surface of the membrane's electrode as well as the screening effect of Cl- on the chloride electrode surface.