Cemented carbide tools having a long life time for copper and copper alloys have so for been needed. Then, the interfacial reaction at elevated temperature between pure copper (tough pitch copper) and titanium carbide (TiC) or titanium nitride (TiN) layer deposited on WC-Co substrate by CVD or PVD was examined using diffusion couples prepared at 1273 K to know whether the layer was effective to check the reaction or not. It was found that two sorts of layers, in no relation to the coating methods, did not almost react with pure copper. It was observed that titanium atoms diffused out from each layer to absorb oxygen or nitrogen, leading to the formation of extremely thin titanium layer with dissolved oxygen or nitrogen at the interface. In the application of cemented carbide tools for copper and copper alloys, the TiC or TiN coating was suggested to be very useful.