In this paper, carbon nanotubes were used as the reinforcements in the polymer composites for the application of electromagnetic interference, due to their outstanding mechanical and electrical properties. The multi-walled carbon nanotubes (MWNTs) synthesized by the chemical vapor deposition method were used to reinforce the epoxy resin by both mixing and spreading processes. The effects of the weight percentage and the reinforced form of MWNTs on electromagnetic interference shielding effectiveness, including the absorbance and the reflectance, were investigated. From experimental results, the electromagnetic shielding effectiveness of the nanocomposite specimens is improved with increasing content of MWNTs. The nanocomposites fabricated by the spreading process have better shielding effectiveness than those made by the mixing process. The nanocomposites, made by the spreading process with 2 wt% MWNTs, had up to 22.69 dB of electromagnetic shielding effectiveness. The reflectance percentage of electromagnetic shielding increases for higher content of MWNTs. The layerwise form of MWNTs in the nanocomposites, resulting from the spreading process and having a better electromagnetic shielding effectiveness, can be observed from the morphologies of the tensile failure surfaces of the nanocomposite specimens by filed emission scanning electron microscopy.