The electrochemical behaviors of anthraquinonedisulphonate (AQDS) dissolved in solution and incorporated into polypyrrole (PPy) matrix as doping species at PPy modified glassy carbon (GC) electrode were investigated in detail, also reported was their applications in the electrocatalytic reduction of oxygen. It was found that the redox process of AQDS in solution and doping phase both exhibit quasireversible behavior and pH dependence. The value of ionization constant pK(a) for the H(2)AQ/HAQ(-) couple increases obviously from 7.6 in solution phase to 9.5 when AQDS is incorporated into PPy matrix. Under optimum condition (pH 6.0), the reduction of oxygen at the GC/PPy/AQDS electrode (AQDS in doping phase) occurs irreversibly at a potential about 621 mV less negative than at a bare GC electrode. The same peak potential shifts 78 mV to more positive potential when compared with the response for AQDS in solution phase. The observed electrocatalysis for the reduction of oxygen is mediated by the electrochemical reduction of AQDS. The number of electrons involved n and the kinetic parameters such as electron transfer coefficient alpha, catalytic reaction rate constant k, k(f) and the diffusive coefficient of oxygen Do,, were determined by using various electrochemical approaches. The stability of the catalytic activity for the GC/PPy/AQDS electrode was also examined. (c) 2006 Elsevier B.V. All rights reserved.