Potassium niobate (KNbO3) microcubes with cubic crystalline phase were hydrothermally prepared and deposited with gold nanoparticles. The structural and electronic properties of the as-prepared samples were studied by X-ray diffraction, X-ray photoelectron spectroscopy, diffuse reflectance UV-visible spectroscopy, scanning electron microscopy, transmission electron microscopy and high-resolution transmission electron microscopy. The catalytic property of Au/KNbO3 was evaluated toward hydrogen peroxide (H2O2) decomposition in dark and methylene blue (MB) degradation under visible-light ( lambda > 420 nm), respectively. At the same Au contents, increasing reaction pH from 7 to 12 can dramatically promote H2O2 decomposition by a factor of ca. 18. With the increase of Au particle size from 4.2 to 10.0 nm at the same pH, the reaction rate constant was increased as well. The underlying mechanism responsible for the observed catalytic performance was discussed in terms of Au particle size, reaction pH, the interaction between Au and KNbO3, and the catalytically active sites at the interface between Au and KNbO3. Likewise, MB degradation was shown to be Au particle size-dependent. Increasing Au particle size from 4.2 to 10.0 nm can enhance MB degradation that is mediated by visible-light-induced surface plasmon resonance on Au nanoparticles. (C) 2013 Elsevier B.V. All rights reserved.