The effect of the substrate on the mechanical properties of a deposited film was demonstrated to be dependent on the interfacial adhesion strength. Three different techniques, namely the micro-indentation, microscratch and load relaxation rests, were used to investigate the mechanical properties of a model system, which was comprised of 1μm aluminum films deposited on Si<100> substrates where one of the samples had a deliberately weakened adhesion strength. It showed clearly that the weakened interfacial adhesion was responsible for the decreases in the composeite hardness, contact stiffness and scratch resistance and the increase in the relaxation rate of the aluminum film as well. The observed results are explained qualitatively in terms of the confinement of the yield zone by the film-substrate interface. The involvement of interfacial cracks is also demonstrated and discussed. © 1990.