Poly(aniline-co-2,4-diaminophenol) (PADAP) was synthesized in a solution containing aniline, 2,4-diaminophenol (DAP) and sulfuric acid, using potentiostatic method. The image of a PADAP film is constructed of spherical particles with an average diameter of 50 nm, which was examined by both scanning electron microscope (SEM) and atomic force microscopy (AFM). The nanostructured PADAP can catalyze xanthine oxidation under a less positive potential of 0.31 V (vs. SCE), which was proved by cyclic voltammetry and amperometric method. The PADAP electrode has a very fast response for the determination of xanthine. The response current of the PADAP electrode increases with increasing xanthine concentration and applied potential. The catalytic mechanism for the oxidation of xanthine on the nanostructured PADAP electrode is similar to that of xanthine oxidase-catalyzed reaction. Experimental evidence for the electrocatalytic mechanism of xanthine oxidation on a PADAP electrode was demonstrated via measurements of the open-circuit potential and the in situ chemical-ESR spectra of PADAP in the solutions without and with xanthine, respectively. (C) 2010 Elsevier Ltd. All rights reserved.