In this work, we systematically studied the CO oxidation on a MgO(1 0 0) supported PtxAu3-x clusters via Langmuir-Hinshelwood (LH), trimolecular Langmuir-Hinshelwood (3LH), and Eley-Rideal (ER) mechanisms on the basis of density functional theory (DFT) calculations. It is found that the Pt2Au1/MgO cluster possesses the highest catalytic activity relevant to CO oxidation, which is considered to be the best catalyst among these supported subnanometer PtxAu3-x clusters. We expect that computational screening of mechanism-dependent properties of sub-nanocatalysts in this work could be useful in the design of highly efficient nanocatalysts. (C) 2015 Elsevier B.V. All rights reserved.