A finite element method was developed to predict the effective thermal conductivity of particle filled epoxy composites. Three-dimensional models, which considered the effect of filler geometry, filler aspect ratio, conductivity ratio of filler to matrix, and interfacial layer were used to simulate the microstructure of epoxy composites for various filler volume fractions up to 30%. The calculated thermal conductivities were compared with results from existing theoretical models and experiments. Numerical estimation of ellipsoids-in-cube model accurately predicted thermal conductivity of epoxy composites with alumina filler particles. The number of length division during mesh process and particle numbers used in the finite element analysis affect the accuracy of calculated results. At a given value of filler content, the numerical results indicated a ratio of conductivity of filler to matrix for achieving the maximum thermal conductivity.