Nanocrystalline Cu-Cr mixed oxides catalysts with different molar ratios of Cu/Cr were synthesized by the hydrothermal method and employed in the catalytic CO oxidation. The physicochemical properties of these catalysts were characterized by powder X-ray diffraction (XRD), N-2 adsorption (BET), temperature programmed reduction (TPR), scanning and transmission electron microscopy (SEM and TEM) methods Also, for a better comparison of catalysts the reaction rate and TOF values were calculated at two different temperatures. The results represented that the powders were mainly consisted of macropores with wide pore-size distribution. The catalytic results showed that the activity of the sample with a Cu/Cr molar ratio of 2 was significantly higher than the other samples due to the formation of CuCr2O4 spinel structure, which was more active than the CuO and Cr2O3 phases in CO oxidation reaction. (C) 2017 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.