Dynamic mechanical analysis and dielectric relaxation spectra of conductive carbon black reinforced microcellular EPDM vulcanizates were used to study the relaxation behavior as a function of temperature (-90 to +100 degrees C) and frequency (0.01-10(5) Hz). The effect of filler and blowing agent loadings on dynamic mechanical and dielectric relaxation characteristics has been investigated. The effect of filler and blowing agent loadings on glass transition temperature was marginal for all the composites (T-g value was in the range of -39 to -35 degrees C), which has been explained on the basis of relaxation dynamics of polymer chains in the vicinity of fillers. Strain-dependent dynamical parameters were evaluated at dynamic strain amplitudes of 0.07-5%. The nonlinearity in storage modulus has been explained based on the concept of filler-polymer interaction and interaggregate attraction (filler networking) of carbon black. The variation in real and complex part of impedance with frequency has been studied as a function of filler and blowing agent loading. Additionally, the effect of crosslinking on the dielectric relaxation has also been reported.