Isotactic polypropylene and elastomeric stereoblock polypropylene nanocomposites containing 0.1-3.5 wt % multiwall carbon nanotubes (MWCNTs) have been synthesized via the in situ polymerization approach using MAO-activated C-2- and C-1-symmetry ansa-zirconocenes, a technique that has not been previously reported in literature. Fracture morphology examination of the nanocomposites revealed very efficient distribution of the MWCNTs within the isotactic polypropylene matrix, yet interfacial adhesion level and the reinforcement efficiency were dependent on the nanotube loadings. The elastomeric stereoblock polypropylene/MWCNT and the isotactic polypropylene-based nanocomposites exhibited different morphologies depending on the synthesis peculiarities. For isotactic polypropylene, Young's modulus increased by similar to 22% even at 0.1 wt % MWCNT loading, and further modulus growth was observed at higher filler contents. Relatively low permittivity values and considerable dielectric losses in microwave range infer that the obtained nanocomposites can find use as efficient electromagnetic shielding materials and microwave absorbing filters. Outstanding improvement of thermal stability (similar to 60 degrees C at maximum weight loss rate temperature) has been achieved for isotactic polypropylene upon incorporating only 3.5 wt % of carbon nanotubes.