The dispersion of multiwalled carbon nanotubes (CNTs) in an ethylene propylene rubber matrix was investigated using an internal mixer. Poly(ethylene-co-polyvinyl acetate) (EVA) statistic copolymer was used as a dispersing agent. The effects of the concentration of the dispersing agent and the matrix viscosity on the quality of the dispersion of 1 wt % of CNTs were studied by using microscopy and rheology in the melt state. It was demonstrated that the dispersion is governed principally by the viscosity of the matrix. As expected, better dispersion was observed when the matrix exhibited a lower viscosity. The influence of the filler content on the rheological and electrical properties is presented. A Cross model with a yield stress is proposed to describe the rheological behavior of these materials, which exhibit a viscoelastic solid behavior from 1 wt % CNT content. Electrical measurement data indicate that the electrical percolation threshold was 2.9 wt %. (C) 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 49: 1597-1604, 2011