The application of NiW substrates for YBCO coated conductor is hindered due to their roughness of surfaces. It was demonstrated that the smooth NiW substrate surfaces can be obtained through electropolishing in a sulfuric acid electrolyte. In this paper, the parameters in the electropolishing process, such as electrolyte temperature, current density and time, are optimized so as to attain the best surface brightness measured by an atomic force microscopy. The et ectropolishing mechanism was discussed on the film generated during the electropolishing process. The results suggest that the electropolishing behavior of NiW alloy is under mass-transfer control and H2WO4 is the governing factor for the film formation mechanism during anodic dissolution. (C) 2012 Elsevier B.V. All rights reserved.