Modulated thermoreflectance microscopy is applied to a complete thermal characterization of a thin film of gold (78 nm) or YBaCuO (300 nm) on a LaAlO3 substrate. The phase profile, measured at several modulation frequencies covering an appropriate range, is fitted with a rigorous thermal diffusion model. This leads to a simultaneous estimation of the thermal diffusivities of the film and the substrate, as well as of the thermal film/substrate boundary resistance. The estimated values for the gold film sample are, respectively, 4.3×10-6 m2 s-1 (substrate diffusivity), 1.0×10-4 m2 s-1 (film diffusivity), and 1.0×10-8 m2 KW-1 (thermal boundary resistance), while for the thermally anisotropic YBaCuO film sample are, 4.1×10-6 m2 s-1, 3.5×10-6 m2 s-1 (in-plane diffusivity), and 8.0×10-8 m2 KW-1, respectively. © 1999 American Institute of Physics.