A series of bimetallic Pt-Au thin films with different Pt/Au ratios were fabricated on glassy carbon (GC) substrates through galvanic replacement reactions between hierarchical Co thin films prepared by cyclic voltammetric deposition and mixed solutions of HAuCl4 and H2PtCl6. The morphologies of the as-prepared Pt-Au thin films resemble those of the sacrificial Co templates, and the Pt/Au ratios in the films are dependent on the HAuCl4/H2PtCl6 molar ratios in the mixed solutions. Because of good stability and excellent synergistic effect of Au and Pt, the bimetallic films with novel structures display unexpected high catalytic activity for the oxidation of formic acid. The as-prepared hierarchical Pt-Au micro/nanostructures are expected to find applications as catalysts in direct formic acid fuel cells (DFAFCs). (C) 2011 Elsevier B.V. All rights reserved.