In this paper, orthorhombic tungsten trioxide monohydrate nanosheets in high yields were successfully generated using a very simple sonochemical method with tungsten hexachloride as the precursor and distilled water as the solvent. The tungsten trioxide monohydrate nanosheets exhibited thickness of about tens of nanometers and edge length of up to several hundreds of nanometers. The sheet-like morphology has been well explained based on the acoustic cavitation effect as well as the crystalline structure of orthorhombic tungsten trioxide monohydrate. The tungsten trioxide monohydrate nanosheets sensor exhibited ideal room-temperature gas-sensing performances, and were found to be sensitive to various flammable organic vapors and harmful gases. The corresponding sensing mechanisms were also discussed. (C) 2010 Elsevier B.V. All rights reserved.