Iron oxide nanoparticles (NPs) were prepared via a simple hydrothermal method for high performance CO gas sensor. The synthesized alpha-Fe2O3 NPs were characterized by X-ray diffraction, nitrogen adsorption/desorption isotherm, scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), and selected area electron diffraction (SAED). The SEM, TEM results revealed that obtained alpha-Fe2O3 particles had a peanut-like geometry with hemispherical ends. The response of the alpha-Fe2O3 NPs based sensor to carbon monoxide (CO) and various concentrations of other gases were measured at different temperatures. It found that the sensor based on the peanut-like alpha-Fe2O3 NPs exhibited high response, fast response recovery, and good selectivity to CO at 300 degrees C. The experimental results clearly demonstrated the potential application of alpha-Fe2O3 NPs as a good sensing material in the fabrication of CO sensor. (C) 2015 Elsevier Ltd. All rights reserved.