A reflux-treatment of soluble polyaniline(SPA)in dimethylformamide(DMF)containingCoCl_2 yields an active catalyst for dioxygen reduction which can be adsorbed on the electrode surfacefirmly.The catalytic reduction of dioxygen at the glassy carbon(GC)electrode modified by the cata-lyst was studied with cyclic voltammetry(CV),rotating disk electrode(RDE)and rotating ring-diskelectrode(RRDE).The kinetic process of dioxygen reduction at the modified electrode was analyzedwith a new RRDE theory dealing with a nondiffusion-controlled process on ring electrode.The rateconstants for each scheme of dioxygen reduction were calculated,showing that only 2-electron reductionto H_2O_2 was conducted at the modified electrode.The effect of solution acidity on the electrocatalyticbehaviour for dioxygen reduction was investigated.A possibility of initiating catalytic activity fordioxygen reduction was explored with ESCA method.