A gold electrode modified by 5-{[4-(4-mercapto)phenylmethoxy]phenyl}-10,15,20-tris(phenyl)porphyrin cobalt(II) (MPPTPCo(II)) has been prepared. The properties of the modified electrode were investigated by scanning electronic microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) as well as electrochemical methods. The MPPTPCo(II)-SAM (SAM: self-assembled monolayer) modified electrode could successfully be used for the electrocatalytic oxidation of ascorbic acid (AA). The catalytic currents increased linearly with AA concentration in the range of 1.2 x 10(-8)-3.9 x 10(-5) Mol l(-1) with the correlation coefficient of 0.9944. The detection limit was 2.6 x 10(-9) mol l(-1) with 10 min accumulation. (C) 2002 Elsevier Science B.V. All rights reserved.