Polymer matrix composites filled with inorganic particles provide design flexibility in producing advanced materials. The cooperation of the polymers and the inorganic particles helps to improve mechanical, physical and optical properties of the composites. However, the size of the particles is very effective in improvement of the properties of the polymers. Nano particles are generally successful in achieving higher performance but sometimes they may be insufficient because of their tendency to agglomerate during melt mixing. On the other hand, micro particles may give weak surface adhesion with polymers. In this study, micro and nano particles of titanium dioxide, zinc oxide and calcite were used to improve mechanical properties of polypropylene (PP). Composites were prepared on a twin screw extruder and maleic anhydride grafted styrene ethylene butylene styrene (SEBS-g-MA) was also used during melt mixing. Thermal analyses, mechanical tests and morphological investigations of the composites were obtained. The obtained results showed that polypropylene filled with nano particles gave better elastic modulus and tensile strength than that of PP filled with micro particles. Impact strength decreased due to the stiffness of the particles but the presence of the SEBS-g-MA increased the impact strength.