Potassium niobate (KNbO3) submicro-crystals with cubic and orthorhombic phases were hydrothermally prepared and characterized by powder X-ray diffraction, micro-Raman spectroscopy, Fourier transform infrared spectroscopy, nitrogen adsorption desorption, diffuse reflectance UV visible spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, and high-resolution transmission electron microscopy. The photocatalytic performance of the as-prepared KNbO3 samples was evaluated toward H-2 generation from an aqueous methanol solution under UV. The surface area-normalized rate of H-2 production over submicro-cubes with cubic phase is two times larger than that of submicro-rods with orthorhombic phase. In addition, both cubic and orthorhombic KNbO3 submicro-crystals showed much higher reactivity than commercial KNbO3 bulk-like powders. The underlying mechanism was discussed in terms of crystal structure and electronic structure. The results from this study are potentially applicable to a range of perovskites useful in water splitting as well as other areas of heterogeneous photocatalysis. Copyright (C) 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.