The aim of this study is to investigate the effect of various filler materials such as talc, glass bead (GB), and bentonite on sound insulation efficiency of polypropylene (PP). In order to evaluate sound insulation properties of PP-based composites sound transmission loss (STL) was determined. Polypropylene based-composite granules were produced by using twin-screw extruder. Some test specimens were obtained by injection molding process. bentonite filled PP composite exhibited the highest STL values for 100, 200, 400, 500, and 800 Hz. While talc and bentonite loadings at 40 wt% into PP increased the flexural strength of PP, GB loading decreased the flexural strength of PP. Izod notched and unnotched impact strength of PP decreased by loading talc, bentonite, and GB into PP.