In this work we propose a new constitutive theory to estimate the stressstrain response and the softening induced by the Mullins effect during the stretching of filled elastomers. In this study, we used the Mullins and Tobin concept where the filled elastomers are treated as composites with hard-domains and soft-domains and the softening is due to the hard domain transformation into soft domain during stretching. Gent strain energy is assumed to represent the behavior of the unfilled elastomers. This strain energy representation is then reformulated in order to consider fillers effect in the case of filled elastomers. The proposed approach takes into account the effect of the type of carbon-black filler and of its volume fraction on the mechanical response and microstructure evolution during stretching. The predicted results are compared to Mullins and Tobin experimental data, and good agreements are obtained. (C) 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012