The search for earth-abundant semiconductors and co-catalysts for wateroxidation is an important step towards conversion of solar energy into fuel chemicals in a sustainable manner. Here, we report the integration of Co3O4nanoparticles within graphitic carbon nitride to construct a nanohybrid photocatalyst made of abundant elements for the photocatalytic generation of oxygen from water, achieving an apparent quantum efficiency of 1.1% at 420 nm for water splitting to oxygen. The present system shows great promise in polymer photocatalysis for applications in future energy cycles based on sustainable materials.