A covalently attached multilayer film containing cobalt phthalocyanine was fabricated on the surface of a glass carbon electrode by UV irradiation of ionic self-assembled multilayer films of a diazo-resin and cobalt phthalocyanine tetrasulfonic acid tetrasodium salt (CoTsPc). The multilayer films have been characterized by UV, IR spectra and cyclic voltammetry. The modified electrode had an excellent electrocatalytic response to the oxidation of hydrazine at a potential where oxidation of hydrazine is not observed at a bare glassy carbon electrode in alkaline aqueous solution. The modified electrode also exhibited several attractive features, such as simple preparation, fast response, good stability and repeatability, so it can be applied as an amperometric sensor of hydrazine. (C) 2003 Elsevier Science B.V. All rights reserved.