The use of a glassy carbon electrode coated with a Nafion perfluorosulphonate resin containing N,N′-bis(3-carboxysalicylidene)trimethylenediamine (a Schiff base) in anodic stripping voltammetry for the determination of trace amounts of mercury is described. The coating procedure, performed by applying a solution of the polymer containing the Schiff base to the electrode surface, is convenient and fast. In comparison with the glassy carbon electrode, the main advantages of the modified electrode are improved resistance to interference from surface-active compounds and increased sensitivity and selectivity. The utility of the modified electrode was demonstrated by its application to samples of urine and natural water.