Au nanoparticles are highly dispersed on Mg-Al mixed oxides by anion exchange (Au/MAO-AE) and homogeneous deposition-precipitation (Au/MAO-HDP). The XRD, UV-visible, and XPS spectra demonstrate that the Au species on both samples are present as metallic Au. The Au nanoparticles are directly confirmed by the transmission electron microscopy images. Very importantly, both Au/MAO-AE and Au/MAO-HDP catalysts show superior catalytic activity, selectivities, and recyclabilities in the aerobic homocoupling of phenylboronic acid, yielding biphenyl and phenol. During this reaction, H2O molecules from the system and hydroxyl groups on Mg-Al mixed oxides strongly influence the catalytic performance. Based on the catalytic data and XPS characterizations, a mechanism for aerobic homocoupling of phenylboronic on metallic Au nanoparticles is proposed. These catalytic data are in good agreement with those obtained from theoretical calculations. (C) 2012 Elsevier Inc. All rights reserved.