As a photocatalyst for solar water splitting, niobium-substituted silver tantalate (AgTa0.7-Nb0.3O3) modified with platinum (Pt) and cobalt phosphate (Co-Pi) was synthesized by a combination of hydrothermal synthesis and photodeposition. Under simulated solar light, AgTa0.7Nb0.3O3 could split water into hydrogen and oxygen in a stoichiometric ratio, and enhancement of the reaction rate owing to the cocatalyst deposition was observed. In particular, co-loading of Pt and Co-Pi considerably enhanced the photocatalytic activity, whereas the enhancement was moderate when either was loaded alone. A possible mechanism for the enhancement is explained based on the band position of AgTa0.7Nb0.3O3 against redox potentials for hydrogen and oxygen evolution. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.