A one-step template-free hydrothermal route has been successfully developed to synthesize monoclinic W03 (m-W03) nanoplates through a topochemical conversion process. The crystal structures and morphologies of the products were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and high resolution TEM (HRTEM). The optical properties of the m-W03 were studied by means of UV-vis diffuse reflection absorption spectra and photoluminescence (PL) spectra. The Brunauer-Emmett-Teller (BET) surface areas of the products were obtained from the N2 adsorption-desorption measurements. The results show that the m-W03 nanoplates are about 100-170 nm in side length and 30-50 nm in thickness. This product exhibits superior photocatalytic activity for the degradation of rhodamine B (RhB) under visible light irradiation, which may be attributed to its high crystallinity and high BET surface area. After calcination at 600 C for 2 h, the W03 catalyst shows a much enhanced activity, 4.7 times higher than the commercial W03 powder, which may be related to the high concentration of the active species "OH in the catalytic reaction system. (C) 2014 Elsevier B.V. All rights reserved.