Using first-principles methods, we investigated the reaction pathways of the formic acid oxidation on Pd(111) and PdAu(111) surfaces. The dehydrogenation of formic acid can simultaneously occur via C-H and O-H activation on different Pd ensembles. However, on the contiguous ensembles without threefold Pd hollow, the reaction of COOH -> CO + OH proceeds with a high activation energy (similar to 1.00 eV), and the direct pathway is predominant for H production from formic acid. Our results indicates that the proper arrangement of Au and Pd sites can significantly improve electrocatalytic activity of PdAu catalyst for formic acid oxidation attributed to the reduction of poisoning species of COad. (C) 2012 Elsevier B.V. All rights reserved.