This paper study the effect of the calcium carbonate (CaCO3) nanoparticleson mechanical and physical properties of virgin and waste polypropylene (pp.). 3, 5, 7 and 10 (wt. %) of CaCO3nanoparticles are mixed with each of virgin and waste pp.These mixture are blended in co-rotating twin screw extruder at 190 °Cand different screw speed (25 and 50 rpm). Different mechanical and physical technique are used to evaluate the characteristics of polymer nanocomposites ex: Tensile strength , elastic modulus , impact strength , hardness and density. The results of virgin pp./(CaCO3) showed that The tensile strength decreasing with nano(CaCO3) concentration for virgin pp. , while for waste increasing at 5% and then decreasing gradually. The impact strength increasing with nanoCaCO3concentration increasing. The hardness and density increasing with the increasing of the nanoCaCO3concentration for two type of pp.Nearly all the mechanical properties were found to increase with the processing speed of 25 rpm. In this studies, it was seen that the highest processing speed of 50 rpm does not give the material performance enhancements due to higher shear intensity which causes defect points in the structure. Also the time is smaller at high screw speeds, so there is not enough time for good dispersion to occur.