In order to prepare a biosensor for the determination of xanthine, electropolymerization of pyrrole on Pt surface was carried out with an electrochemical cell containing pyrrole, ferrocene (as a electron mediator) and tetrabutylamonium tetrafluoroborat in acetonitrile by cyclic voltammetry between 0.0 and 0.9 V (vs SCE) at a scan rate of 50 mV/s upon Pt electrode. Xanthine oxidase was immobilized by a glutaraldehyde/bovine serum albumin (BSA) crosslinking procedure on to polypyrrole film after the electropolymerization processes. The response of the biosensor against xanthine was measured after 3-4 min following the application of a constant potential of +0.7 V (vs SCE). The resulting biosensor exhibits excellent electrocatalysis for the xanthine. The amperometric determination is based on the electrochemical detection of H2O2 , which is generated in enzymatic reaction of xanthine. The effect of various experimental conditions was examined for the determination of the analytical performance. The sensor responds to xanthine with a detection limit of 1.0 x 10(-6) M. The response current increases linearly with xanthine concentration up to 4.0 x 10(-4) M. The sensor remains relatively stable for 45 days.