The simultaneous control of morphology of Dy-Ni alloy was achieved by selective anodic dissolution of Dy in a molten LiCl-KCl-DyCl3 (0.50 mol %) system at 700 K. The electrochemically formed DyNi2 films, about 20 mum thick, were transformed to porous Dy2Ni7, DyNi5, and Ni films, depending on the applied potential. Larger pores were formed when the applied potential was more positive. The rapidity and the pore-forming mechanism of the process are suggested to be closely related to the existence of the grain boundary in the alloy because the transformation reaction was very slow for the annealed DyNi2 electrode. (C) 2002 The Electrochemical Society.