In this work, composites of isotactic polypropylene (PP) with three unvulcanized elastomers - terpolymer of ethylene-propylene-dicyclopentadiene (EPDM), chlorinated polyethylene (CPE) and copolymer of acrylonitrile-butadiene (NBR) - have been investigated. The purpose of the investigation was to create PP/elastomer blend composites of significantly different compositions (with an excess of PP, intermediate ones, and with an excess of elastomer) and to study the dependence of tensile behaviour and elastic properties on the blends with different component ratio. Tensile properties have been recognized from the stress-strain curves. The changes of elastic modulus have been characterized with respect to the Hashin-Shtrikman upper and lower bounds and the Davies equation. Calorimetric properties of PP blends with elastomers (crystallinity and melting behaviour of polypropylene phase) have also been investigated with the method of differential scanning calorimetry (DSC).