In this paper, the numerical homogenization technique is used to evaluate the representative volume element and to compute the effective transverse thermal properties of unidirectional fibers reinforced composites. Three unit cells are constructed including square, hexagonal and random arrangement. The results obtained by finite element analysis showed the effect of unit cells configurations on the prediction of effective transverse thermal properties of unidirectional fibers composites for a wide range of fiber volume fractions and contrasts of properties. The numerical results are compared to available analytical models in the thermal conductivity of composites and experimental test results from the literature.