Abstract:-This work investigated the morphological and rheological behavior of calcium carbonate (CaCO3) nanoparticles reinforces virgin polypropylene and its waste. The reductions in the global properties especially the rheological behavior as a result of structure degradation are essential issue in reusing the waste thermoplastic polymer. The mixing of nanoparticles with polymer melts giving significant changes in the flow and physical properties. CaCO3 nanoparticles are mixed in different concentrations 3, 5, 7 and 10wt % with the virgin polypropylene and its waste by melt compounding in a twin screw extruder at different screw speeds (25and 50) rpm and 190°C. Different microstructure and morphological techniques (X-ray Diffraction and field emission scanning electron microscopy) were used to evaluate the effect of the CaCO3 nanoparticles concentrations on the microstructure of the nanocomposite, also melt flow rate (MFR) and melt volume rate (MVR) were tested using melt flow index (MFI) device. MFR of the polymer nanocomposite was examined due to the nanoparticles concentration, loads, temperatures and rotating speed changes, while MVR was tested at different CaCO3 nanoparticles concentrations at standers load (2.16kg). Shear rate and viscosity were predicted according to the MFR values. The results show that the crystallinity level was increasing with the CaCO3 nanoparticles percentage increasing for virgin and waste polypropylene. The CaCO3 nanoparticles distribution in polypropylene matrix at 25 rpm is more homogenous and less agglomeration than at 50 rpm.