Abstract- Materials which offer the combination of high damping and stiffness are attractive for many industrial applications. In this work the stiffness and damping properties of Polypropylene/Calcium-Carbonate (PP/CaCO3) nanocomposites have been studied. In order to improve the dispersion of CaCO3 nanoparticles in polypropylene matrix, nanoparticles were coated by monolayer of stearic acid. All samples containing 5, 10, 20 and 30 wt% nanoparticles were mixed in co-rotating twin screw extruder and were formed into sheet by hot press, then standard tensile specimens were provided by pneumatic punch. Tensile properties of samples were experimentally investigated. To examine dynamic mechanical properties we use DMTA and Morphology of samples was performed by SEM. SEM images showed a suitable dispersion of coated CaCO3 nanoparticles by monolayer of stearic acid. The results of tensile test showed that with growth of nanoparticles weight percent, tensile strength decreases and young’s modulus increases. According to the results of DMTA, damping properties of samples improve with the growth of CaCO3 nanoparticles.