A simple low temperature hydrothermal method has been investigated for synthesis of single phase hexagonally plate ZnO microstructure. The synthesized ZnO was characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) photoluminescence spectrum (PL) and ultraviolet and visible absorption spectroscopy (UV-vis) to investigate the surface morphology, crystallographic phase, optical properties and used as a sensor for detection of CO gas molecules. It was observed that the ZnO microstructures were uniform size, single phase and symmetrical, with a hexagonal shape and height of similar to 250 nm. The optical band gap value of this sample was calculated to be about 3.22 eV, which show a red shift with theoretical method. High-resolution TEM images indicate that all the microstructures are single crystals with a [001] direction growth. We studied the gas response of this sample to 500 ppm CO over a temperature range of 200-400 degrees C and compared with theoretical results. Density functional theory (DFT) calculations were employed to investigate the structure and electronic properties of ZnO with simulating the adsorption process of CO gas on the ZnO (101) surface. The theoretical results were in good agreement with experimental results. (C) 2014 Elsevier B.V. All rights reserved.