Preparation of fine TaON particles is attempted to improve the photocatalytic activity for H-2 evolution from aqueous methanol solution under visible light (lambda > 420 nm). TaON is synthesized by nitriding Ta2O5 powder at 1123 K for 15 h under a flow of NH3. When nanoparticulate Ta2O5 with a primary particle size of 30-50 nm is used as the precursor, fine particles of TaON (FP-TaON) with 50-80 nm in size is obtained, but the primary particles aggregate to form larger secondary particles. Nitridation of Zr-Ta mixed oxide (Zr/Ta=0.1) nanoparticles results in the production of a solid solution of monoclinic-ZrO2 and TaON exhibiting 30-50 nm primary particle size with less aggregation and higher activity, as compared to FP-TaON. Suppression of surface defects (reduced tantalum species) produced during nitridation from Ta2O5 to TaON is shown to be essential for achieving efficient H-2 evolution using TaON-based photocatalysts. (C) 2009 Elsevier B.V. All rights reserved.