Diamond films were synthesized on smooth Si (100) and cemented carbide inserts with 8% cobalt by chemical vapor deposition (CVD). Molybdenum was evaporated on the substrate after diamond had nucleated. The effect of molybdenum on the morphology, crystal structure, non-diamond phase, film/substrate interface and adhesion of diamond films was investigated. The result shows that the effect of molybdenum on the quality of modified diamond films (diamond films with molybdenum) is not evident when the thickness of molybdenum is less than 0.5 mum. The evaporated molybdenum could not only hinder cobalt to diffuse from the bulk to the surface, but also fill in the micro-pore between diamond film and substrate. The adhesion of modified diamond films is better than that of the conventional. (C) 2004 Elsevier B.V. All rights reserved.