The redox process between molecular oxygen, O-2, in an aqueous solution, W, and tetrachlorohydroquinone, CQH(2), in 1.2-dichloroethane, DCE, at the W \ DCE interface was investigated by electrolyses at different potential differences applied between the two phases, E-appl. Three different overall redox reactions were found to occur depending on E-appl. After electrolysis, the final reduction products of O-2 in W were H2O as well as a small amount of H2O2 and the final oxidation products of CQH(2) in DCE were the tetrachloroquinone anion radical, CQ(-.), for one range of E-appl, H2O as well as H2O2 and tetrachloroquinone, CQ, for a second range, and H2O2 and CQ for a third range. The redox processes were elucidated taking into account the results obtained by polarography for charge transfer at the W \ DCE interface in addition to the results mentioned above. It was also demonstrated that redox reactions between O-2 and CQH(2) could be realised and controlled, not only by the electrolysis, but also by ion transfer reactions at the interface coupled with the redox reactions.