Precise quantification of the adhesion of diamond coatings on cemented carbide (WC-Co) inserts is important for industrial applications. Adhesion is strongly influenced by the surface roughness, surface reactivity, catalytic effect of Co during diamond chemical vapour deposition (CVD) and by stresses developed in the Nm and at the bonding interface. In this work we investigated the adhesion of diamond coatings on WC-Co by using Rockwell-C indentation. Various surface modifications were studied : Co leaching; replacement of Co by Cu; WC-Co decarburization and deposition of Ti intermediate layer prior to diamond CVD. Turning tests with diamond coated inserts for machining of Al alloy were carried out.