A stable monolayer of a polymeric ion complex was formed at the air-water interface when dioctadecyldimethylammonium bromide was spread on an aqueous solution of potassium poly(vinyl sulphate). The polyion-complexed monolayer was annealed by a flat-panel heater located above the surface monolayer. The annealed monolayer deposited on an indium tin oxide electrode as a Y-type Langmuir-Blodgett film effectively blocked the electrochemical oxidation-reduction reaction of the ferricyanide ion.