In this study, nanofillers composed of alumina, titania, and organoclay were separately embedded in 50% polypropylene (PP) and 50% ethylene propylene diene monomer (EPDM) blends. Several formulations of PP/EPDM nanocomposites were prepared using an internal mixer and were molded using a compression mold to produce test samples. The effects of filler loading (2, 4, 6, and 8 vol %) on the dielectric breakdown strength, dielectric properties, hydrophobicity, and flammability were determined. The addition of nanofillers improved the breakdown strength (up to 2 vol %) and increased the dielectric constant and dielectric loss of the PP/EPDM nanocomposites. The hydrophobicity of PP/EPDM/Al2O3 increased, whereas the hydrophilicity of PP/EPDM/TiO2 and PP/EPDM/organoclay increased. Flammability test results showed that PP/EPDM/TiO2 had a lower burning rate than PP/EPDM/Al2O3 and PP/EPDM/organoclay. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 41184.