ZnO and Zn0.9Cu0.1O nanoparticles were synthesized by the sonochemical method. Structural and morphological properties of the synthesized nanoparticles were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive analysis of X-ray (EDAX). The results revealed the formation of ZnO and Zn0.9Cu0.1O nanoparticles in wurtzite phase with average crystallite diameter of 30-40 nm calculated from Debye-Scherrer equation. Moreover, the ethanol vapor sensing properties of ZnO and Zn0.9Cu0.1O nanoparticles were investigated at different operating temperatures and they were compared with commercial ZnO microparticles. Comparative results demonstrated that Zn0.9Cu0.1O nanoparticles exhibit highest and fastest response to 250 ppm of ethanol at 300 degrees C. Results on response/recovery time, sensing mechanism, conductance variation and thermodynamics/kinetics of ethanol sensing is also studied and discussed. (C) 2013 Elsevier B. V. All rights reserved.