Monte Carlo computer simulations have been carried out on filled networks of (amorphous) polyethylene and poly(dimethylsiloxane) using a method based on the authors’ general theoretical approach for filled elastomeric materials [Kloczkowski et al., Comput. Polym. Sci. 3 (1993) 39-45]. This approach enables estimation of the effect of the excluded volume of filler particles and non-Gaussian characteristics of the chains on the elastic properties of the filled networks. It is assumed (i) that the filled polymer network consists of a cross-linked mixture of two types of chains, specifically those attached at one end to spherical filler particles and those that are unattached, and (ii) that the elastic modulus of the filled polymer is the sum of contributions from these two types of chains. Distribution functions for the end-to-end vectors of both types of chains were obtained using the Monte Carlo rotational isomeric state technique proposed by Mark and Curro. In the present application, however, conformations of attached chains which overlapped with a spherical particle during the simulation were rejected. The elastic moduli of both types of chains were calculated as a function of the length of the chains, the size of the filler particles, and the temperature.