Glass formation and glass forming ability in the ternary Zr-Cu-Ni system were studied systematically. For Cu mold casting, the critical size for glass formation was found to be 1 mm in a relatively wide composition range of 56-64 at.% Zr, 16-26 at.% 3Cu and 16-24 at.% Ni. The phases competing with glass formation were found to be Zr, Zr2Cu and Zr2Ni. Despite the fact that Cu and Ni are completely miscible with each other, they cannot be regarded as simple substitution to each other in the case of glass formation in the Zr-Zr2Cu-Zr2Ni ternary eutectic system. (c) 2006 Published by Elsevier B.V.