The preparation of polymer nanocomposites by melt compounding polypropylene (PP) with organically modified montmorillonite using maleic anhydride modified PP as compatibilizer is described. Compositions with organomontmorillonite content 0, 5, 10 wt.% were prepared and tested. Data on the influence of organomontmorillonite content on the tensile stress–strain curves, elastic modulus, strength, and ultimate elongation of the nanocomposites are obtained. The concentration dependences of elastic properties of materials with differently oriented plate like nanoparticles analyses taking into account hierarchical structure features of nanocomposites is considered. Theoretical analysis results are compared with experimental data. The presence of unexfoliated particles in the form of multilayer packages must be taken into account. The results of an investigation of hardness, impact strength, and thermal properties of polymer nanocomposites are presented. Tension creep tests were performed to predict nanocomposites long term deformation behaviour.