Compounds of thermoplastic matrices and selective crosslinked rubber are widely used materials in many technical applications due to their specific phase morphology and therefore properties. In particular the modulus does not only depend on the chain density like in conventional rubber but by (i) the crosslink-density of the elastomeric component (EPDM), (ii) the modulus of thermoplastic component (PP) and (iii) the phase morphology, i. e., the particle size. In this paper we investigated the vulcanization kinetics of EPDM as function of the concentration of a sulfur-based crosslinking agent, the crystallization behavior, the phase morphology and mechanical properties of melt-mixed blends of such differently crosslinked EPDM with PP. The kinetics of the vulcanization process was measured by vulcametry, and the rate of vulcanization is a direct function of temperature. Crosslink-densities were calculated from stress-strain-curves and using swelling data. The crystallization behavior of PP is only slightly affected by the rubber component as revealed by differential scanning calorimetry (DSC) and X-ray methods. The modulus, stress and strain at break strongly increase with increasing concentration of the cross-linking agent, which, therefore, seems to be a toot to control final, application-relevant properties.