In this study, hybrid fillers composed of ammonium polyphosphate (APP) and nanoclay were separately embedded in 50% polypropylene (PP)/polypropylene-grafted maleic anhydride (PP-g-MAH) and 50% ethylene propylene diene monomer (EPDM) blends. Several formulations of APP-nanoclay-filled PP-g-MAH/PP/EPDM hybrid nanocomposites were prepared using an internal mixer and were molded using a compression mold to produce test samples. The effects of PP-g-MAH loading (2, 4, 6, and 8 vol.%) on the flammability and electrical insulation properties of APP-nanoclay-filled PP/EPDM hybrid nanocomposites were investigated. The addition of 8 vol.% PP-g-MAH improved the dielectric breakdown strength of the APP-nanoclay-filled PP/EPDM hybrid nanocomposites. The dielectric constant and dielectric loss of the PP/EPDM nanocomposites are found to reduce as PP-g-MAH loading increases. The contact angle measurement shows that the hydrophilicity of APP-nanoclay-filled PP-g-MAH/PP/EPDM hybrid nanocomposites increased. Flammability test results showed that the addition of PP-g-MAH slightly reduced the burning rate and the limited oxygen index of APP-nanoclay-filled PP-gMAH/PP/EPDM hybrid nanocomposites.