The electrolysis of water provides a link between elec. energy and hydrogen, a high energy d. fuel and a versatile energy carrier, but the process is very expensive. Indeed, the main challenge is to reduce energy consumption for large-​scale applications using efficient renewable catalysts that can be produced at low cost. Here we present for the first time that laccase can catalyze electrooxidn. of H2O to mol. oxygen. Native and lab.-​evolved laccases immobilized onto electrodes serve as bioelectrocatalytic systems with low overpotential and a high O2 evolution ratio against H2O2 prodn. during H2O electrolysis. Our results open new research ground on H2O splitting, as they overcome serious practical limitations assocd. with artificial electrocatalysts currently used for O2 evolution.