Due to the increasing importance and wide utilization of composite materials, the paper presents some considerations on the calculation of dielectric permittivity of mixtures. First, some analytical solutions of the problem are presented, and then the results are compared with the numeric solutions obtained with a FEM based software produced by the ANSOFT Corporation. The analytic and numeric results seem to be in good agreement, which means that the software is reliable and can be Used for the simulation of complex structures, for which no analytical solutions are available.