Orthorhombic molybdenum oxide (α-MoO 3) nanobelts were successfully synthesized by the 100-180 °C and 2-20 h hydrothermal reactions of (NH 4) 6Mo 7O 24·4H 2O solutions containing 15 ml 2 M acid (HNO 3, H 2SO 4 or HCl) with no surfactant and template adding. These products were characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) and Raman spectroscopy, and electron microscopy (EM). In the present research, the product synthesized by the 180 °C and 20 h hydrothermal reaction of the solution containing HNO 3 was α-MoO 3 nanobelts with >10 μm long and <200 nm wide. Electrochemistry for hydrogen evolution reactions (HER) and optical properties of the as-synthesized α-MoO 3 nanobelts were characterized by linear sweep voltammetry (LSV) and Tafel plot, including UV-vis and photoluminescence (PL) spectroscopy. These imply that α-MoO 3 nanobelts show satisfied performance for HER, with the 3.75 eV direct allowed band gap (E g) due to the charged transition of O 2p → Mo 4d, including the emission of 437 nm wavelength at room temperature. © 2011 Elsevier B.V. All rights reserved.