Using a combination of dispersing low-cost carbon nanofibers and a small quantity of carbon nanotubes within the polystyrene matrix, we have demonstrated the formation of a novel nanocomposite with superior microstructure and improved electromagnetic interference (EMI) shielding characteristic. This nanocomposite is very promising for use as an effective and practical EMI shielding material owing to its high shielding effectiveness, light weight, low cost, and easy processability.