The rheological properties of the ionic liquid 1-hexyl-3-methylimidazolium chloride ([hmim][CI]) along with that of its mixtures with Cud, which form the corresponding chlorocuprate(I)-based ionic liquids ([hmim][Cu(Cl)(x)]) are reported. In addition, the flow behaviour of these ionic liquids is thoroughly described for the first time. In previous works we have reported that these Lewis-acid-based ionic liquids exhibit high chemisorption capacity towards carbon monoxide which can be employed to design novel ionic liquid-based CO separation processes. Therefore, accurate knowledge of the transport properties is of utmost importance given the considerable influence of viscosity on mass transfer. Results showed that both [hmim][Cl] and [hmim][Cu(Cl)(x)] ionic liquids exhibited shear-thinning non-Newtonian behaviour associated to the presence of a hydrogen-bonding network. However, the onset of shear-thinning progressively shifted to higher frequencies upon increasing temperature for all measured samples. Moreover, a drastic [hmim][Cl] viscosity decrease from 14.2 to 3.98 Pa s was observed after addition of 2 mol CuCl L-1 at 293 K. In addition, the parameters of Cross model that describes shear-dependant viscosity have also been obtained. (C) 2015 Elsevier B.V. All rights reserved.