The growth morphology of diamond films grown on single crystals of SIC and on sintered WC and cubic BN (CBN) substrates by hot filament assisted chemical vapour deposition was examined using transmission electron microscopy and scanning electron microscopy. Diamond was found to have the form of particles on the substrates of SiC and WC in the initial stage of film growth. Both an amorphous layer and a directly bonded a rea were seen at the interface. Several orientation relationships, different from the cube/cube relation, were observed in these systems. On the other hand, in the case of diamond films on CBN substrates, the growth morphology of diamond was affected by the surface condition of the substrates. When CBN substrates were polished with a diamond paste before deposition, diamond grew in the form of particles. The growth morphology was changed by ion sputtering of the surface of the substrate from particle growth to uniform film growth. These results are discussed on the basis of lattice mismatch at the interface.