To improve the efficiency in shielding electromagnetic interference in electronic devices, multi-walled carbon nanotubes were used, due to their excellent electric and magnetic properties at high aspect ratios, and were added to an epoxy matrix. Fluorination was carried out to achieve excellent dispersion and adhesion of the additives in the epoxy matrix. The improved dispersion was confirmed by UV spectra. The permittivity and permeability were also significantly improved based on the effects of the additives and the fluorination treatment. The efficiency of shielding electromagnetic interference increased up to 28dB. This improved efficiency of shielding electromagnetic interference may be caused by a well-organized conductive network of additives in epoxy.