An Au/ZrO2 catalyst was prepared and characterized in order to study the role of gold nanosize in the conversion of furfural into methyl furoate by oxidative esterification with O-2 and methanol, without NaCH3O. The comparison with the Au/TiO2 reference catalyst provided by the World Gold Council and with an Au/ZrO2 catalyst treated at 600 degrees C in oxygen emphasized very good catalytic performances. Highly dispersed Au was evidenced on Au/ZrO2 by quantitative CO chemisorption, HRTEM analysis and FTIR spectroscopy of adsorbed CO. On the contrary, the thermal treatment at 600 degrees C results in the presence of nanoparticles larger than 4 nm that make the catalyst poorly active and selective. The Au clusters and their ability in the activation of the O-2 molecule play a key role in the reaction. (C) 2012 Elsevier B. V. All rights reserved.