Crystalline NaTaO3 nanoparticles doped with different concentrations of La3+ have been synthesized via a H2O2-assisted sol-gel route. In this reaction, TaCl5 is dissolved in aqueous H2O2 solution to form a stable transparent Ta-peroxo complex solution. The formation of tantalum-peroxo complexes and their chelation by citric acid enables a better control of crystal growth. X-ray diffraction and scanning/transmission electron microscopy provide useful information about crystallinity and morphology of the samples. The substitution of La3+ ions in the NaTaO3 lattice is verified by crystallographic simulation (CaRlne Crystallography version 3.1). These results indicate La3+ ions occupy the Na+ ions sites, which agrees very well with the experimental data. The optimal content of La3+ ions effectively increases crystallinity without agglomeration, contributing to efficient charge separation and preventing recombination between photogenerated electrons and holes. The highest photocatalytic H-2 production of 1.43 mmol h(-1) is obtained for a 2.0 mol% La-doped NaTaO3 sample. The NaTaO3 nanoparticles produced using this facile, environmentally friendly 'green process' have better crystallinity, smaller size and higher photocatalytic activity. (C) 2010 Elsevier B.V. All rights reserved.