An electromagnetic radiation shielding material (ERSM) based on carbon nanofiber-reinforced poly(ether-ketone) composite was prepared via corotating twin screw extruder and then injection-molded into dog bone-shaped specimens for testing. In order to design this type of material ERSM, electrical conductivity was targeted as key property using a conducting inclusion, carbon nanofibers (CNFs). Electrical conductivity increased from similar to 10(-13) S/cm for neat PEK to similar to 10(-3) S/cm for samples having 14 vol % (20 wt%) of CNFs, which was close to the requirement for microwave shielding. Nanocomposites are shown to exhibit up to -40 dB (> 99.999 % attenuation) of total shielding effectiveness at 14 vol % (20 wt%) loading in the frequency range of 26.5-40 GHz (Ka band). This formulation of nanocomposites (14 vol % loading) shows shielding effectiveness due to absorption of similar to-37 dB with very less reflection loss of similar to-3 dB in the prescribed frequency range. Achievement of such high absorption-dominant shielding effectiveness (-37 dB) along with high thermal stability (T-0.25 similar to 614 A degrees C) and mechanical strength (tensile strength similar to 112 MPa and tensile modulus similar to 7.2 GPa) substantiates its capability as light weight, thermally stable, and mechanically strong EMI shields for demanding applications such as aerospace, defense, and space applications.