Abstract: Au/C catalysts were prepared by immobilizing the gold sol having a mean particle size of 5.0 nm with a quite narrow size distribution on carbon nanotubes (CNTs), Vxc-72R or ECP 600JD carbon black. Electrocatalytic activities of different Au/C catalysts with and without acid treatment (first with concentrated HCl then with concentrated HNO₃) for the carbon supports for BH^-₄ oxidation were investigated. The hydrophilicity of all carbon supports and the Brunauer-Emmett-Teller (BET) surface area of CNTs increased, but the BET surface area of Vxc-72R or ECP 600JD decreased after the acid treatment. The Au loading on the carbon supports was closely related to the BET surface area of the supports. Acid treatment of the carbon supports was also an important factor for improving the electrocatalytic activity of the catalysts. Au supported by the acid-treated ECP 600JD exhibited the best electrocatalystic activity for BH^-₄ oxidation as an anode catalyst for the direct sodium borohydride fuel cell.