The fabrication of a chemically modified electrode by self-assembled bi-(2-aminoethyl)-aminodithiocarboxyl acid (BADTC) and its further derivatization to form a monolayer of cupric hexacyanoferrate (CuHCF) has been developed. This modified electrode is electroactive and its surface concentration is 4.1 x 10(-10) mol cm(-2), Obtained by using cyclic voltammetry. The apparent surface electron transfer rate constant k(s)(degrees)’ is 0.79 s(-1). It is observed that this inorganic monolayer modified electrode shows an ideal-Nemstian response, with a slope of 60 mV/decade, to potassium ion in the range 1.0 x 10(-2) to 1.0 moll(-1). Moreover, it can be used to discriminate between potassium and sodium ions.