This paper describes numerical investigations conducted on filled rubbers. Some experimental data on stress relaxation tests carried out on various filled elastomers evidenced that increasing the content of rigid particles such as fillers or changes in the crystallization index, result in higher values of the stress relaxation rate. This result seems to indicate that higher rigid particle contents promote macroscopic viscoelastic strain. To better understand this effect, finite element analyses were carried out on axi-symmetric unit cells as well as unit cell for numerical homogenization with periodic computations.