This study investigates the fundamental effects of particle distribution in a heterogeneous composite, which has never been revealed before. This work is based on the Laplace equation in cylindrical coordinates and shows that the effective thermal conductivity has a different value even at the same volume fraction depending on the particle distribution configuration. Consequently, applying the effective medium approximation without using detailed information about the particle spatial distribution can result in considerable error. This is especially true for the case of augmented conduction by insertion particles.