Oxygen reduction at a dinuclear Co(II)-Schiff-base complex, Co(II),-3,3’, 4,4’-tetra(salicylidene imino-1,1’-biphenyl tetrahydrate [Co(II),-disalophen; Co(II)(2)-DSP . 4H(2)O], modified carbon electrodes has been studied and results thereof are reported. The absorbed complex is shown to have a large catalytic effect for oxygen reduction. The oxygen reduction at the Co(II)(2)-DSP . 4H(2)O modified carbon electrodes is reasonably reversible in alkaline solutions with an apparent number of electrons transferred of around one and an estimated exchange rate constant of about 0.04 cm/s. The strong catalytic activity is explained by the formation of a reversible adduct with oxygen, i.e., Co(III)(2)-disalophen 2O(2)(-1), followed by reduction of Co(III) in the adduct. The cyclic voltammetric and chronoamperometric experimental results suggest that the first electron transfer should be a rate limiting step.