This paper develops the general framework for the calculation of thermal boundary resistance between a substrate and a composite. All the previous works on the modeling of thermal boundary resistance have only dealt with pure materials. Thermal boundary resistance is dependent on the phonon equilibrium intensity and the transmissivity of phonons across the interface. These quantities depend on the group velocity, phase velocity and density of states of phonons. Due to multiple and dependent scattering of phonons the group velocity, phase velocity and the density of states are modified in a composite. Modification of these quantities is more dominant for nanocomposites at low temperatures. Results for silicon/germanium nanocomposite show that thermal boundary resistance can be severely modified depending on the temperature and size of the particulates. Results also show that when the particle size becomes large, the thermal boundary resistance between the substrate and the composite is same as that between the substrate and the host matrix of the composite. (c) 2005 Elsevier Ltd. All rights reserved.