The mechanical properties of high-quality cubic boron nitride (cBN) films were systematically investigated by nanoindentation measurements performed in both cross-sectional and plan-view directions. The large film thickness (similar to 5 mum) allows the effective ruling out of both substrate and indenter size effects. The hardness and elastic modulus values were found to be 70 and 800 GPa, respectively, which are the highest values ever obtained on cBN films deposited by either PVD or CVD methods so far (comparable to those reported for cBN crystals synthesized by high-pressure high-temperature methods). The variation of hardness across the cBN film thickness was investigated. In conjunction with the transmission electron microscopic observations, the relationship of the hardness measured with the crystallinity and crystal size/grain boundaries was discussed. (C) 2002 Elsevier Science B.V. All rights reserved.