When irradiated with visible light (lambda > 400 nm) 1 wt % gold-supported ceria nanoparticles generate oxygen from water (10.5 mu mol(.)h(-1)) more efficiently than the standard WO3 (1.7 mu mol(.)h(-1)) even under UV irradiation (9.5 mu mol(.)h(-1)). This remarkable photocatalytic activity arises from a novel preparation method to reduce the particle size of ceria (5 nm) by means of electrostatic binding of Ce4+ to alginate gel, subsequent supercritical CO2 drying, and calcination. The low loading of Au is crucial for the observed high catalytic activity.