Diamond films were deposited on YG(6)(WC-6%Co) cemented carbides with different surface characteristics using hydrogen and ethyl alcohol as the feed gases in a hot filament assisted chemical vapour deposition system. The synthesized diamond films were examined by scanning electron microscopy, X-ray diffraction and Raman spectroscopy. It was found that cobalt near the surface of cemented carbides was very detrimental to diamond deposition and the surface characteristics of substrates had a strong influence on the diamond-substrate adhesion. Grinding test results showed that the adhesion strength of diamond to the lapped substrates of smooth surface micro-topographies was very poor and the films flaked severely during the grinding process. However, the diamond films demonstrated good adhesion to substrates with rough surface micro-topographies.