We studied the cutting performance of diamond-coated cemented carbide cutting tools pretreated using acid etching, Murakami reagent etching, interlayer addition, and boronization techniques. The Rockwell. indentation test indicates that the best adhesion is obtained from the diamond-coated cutting tool pretreated using boronization by forming a boronized cobalt compound layer composed Of CoW2B2, CoWB, and CoB. The end-milling test shows that this sample exhibits the longest lifetime among diamond-coated cutting tools, 26-times longer than that of the uncoated cutting tool. The wearing mechanism of the cutting, tools used is also discussed. During the milling period, the failure of the diamond-coated tool pretreated by boronization was dominated by how the diamond grains were gradually removed from the diamond coating by the workpiece scraps, instead of the peeling off of the diamond coating. This also reveals that the diamond coating exhibits good adhesion and cutting performance. (C) 2003 American Vacuum Society.