Monodisperse WO3 center dot H2O square nanoplates were controlled synthesized under hydrothermal conditions with the adding of malic acid. The powders obtained under two different hydrothermal reaction times were characterized by X-ray powder diffraction (XRD) field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). The thickness of the nanoplates would increase due to the prolongation of reaction time. In addition, the differences of exposure of crystal facets of this orthorhombic WO3 center dot H2O square nanoplates were researched and its influence on the gas sensing properties were also discussed. Gas sensor based on the two obtained WO3 center dot H2O square nanoplates powders was prepared and the gas responses to serious concentrations of C2H5OH gas were carried out. These kinds of nanoplates show excellent ethanol gas sensing and it can be influenced by the crystal facet percentage in nanoplates. This works show great significance to the control synthesis of semiconductor metal oxides and their applications in gas sensor research. (C) 2015 Elsevier B.V. All rights reserved.