In this study, we conducted research to establish a technique for synthesizing diamond film, which have a superior adhesion strength, on a WC-Co alloy, by utilizing the characteristics of multi-layered diamond film. First, the chemical bonding strength between diamond film and substrate was improved by increasing the nucleation temperature at the beginning of coating. Next, the internal stress of the diamond film was reduced by setting the deposition temperature of the diamond film to be lower than that in the conventional method and by making the film multi-layered. By optimizing the conditions of the above procedure, we succeeded in the synthesis of a diamond film which has adhesion strength 30% higher than that of the film synthesized by the conventional technique. (C) 2004 Elsevier B.V All rights reserved.