The modified effective medium approximation model proposed by Minnich and Chen [Appl. Phys. Lett. 91, 073105 (2007)] for the thermal conductivity of nanocomposites is extended for spheroidal inclusions. It is shown that the dependence of the thermal conductivity of nanocomposites on the shape and size of particle inclusions can be described by: (1) the collision cross-section per unit volume of the particles and (2) the mean distance that the energy carriers (electrons or phonons) can travel inside the particles. The predictions of this analytical approach are in good agreement with available data obtained through numerical calculations of the Boltzmann equation. © 2011 American Institute of Physics.