Single-crystalline nanobelts of molybdenum trioxides (MoO3) were grown by a thermal evaporation method of molybdenum metal pellets at ambient pressure in a flow of O-2. The chemical composition, crystalline structure and optical properties of the nanobelts were investigated by various characterization techniques such as scanning electron microscopy, transmission electron microscopy, Raman-scattering, energy dispersive X-ray spectroscopy and UV-vis-NIR spectroscopy. The samples were nanobelts with a width up to 50 mu m, about 85 nm in thickness and from tens to several hundred micrometers in length. The analysis indicated that as-synthesized samples were orthorhombic structured MoO3 grown with [0 0 1] preferred orientation. The fundamental optical absorption edge corresponds to direct allowed transitions with an energy gap located at about 3.01 eV. (C) 2008 Elsevier B.V. All rights reserved.