A model for calculating the V(z) curve by line-focus acoustic microscopy contains the reflectance function of the specimen as a principal component. In this paper, the reflectance function has been analyzed for various film/substrate systems with a non-perfect interface between the film and the substrate. A theoretical study has been carried out to investigate the effect of a non-perfect interface on the propagation of surface acoustic waves (SAW) and its implications for measurements by line-focus acoustic microscopy (LFAM). An experimental study has been performed to verify the theoretical predictions, and to explore the potential of LFAM at high frequencies for non-destructive quantitative evaluation of the bond quality between a film and a substrate. A number of film specimens with different interface conditions between the film and the substrate have been investigated. The stiffness parameters of a non-perfect interface have been determined by the combined use of the V(z) model and LFAM based measurements. The results have been compared with results obtained by other techniques.