Over the last decade, advancements in the electronics sector have raised the bar for EMI shielding requirements. To meet this demand, recent research has focused on developing shielding materials that can give the same level of EMI SE value while eliminating all of the disadvantages of traditionally employed metallic shields. However, there is a significant gap between laboratory-level preparation and industrial applications. In this thesis work, we tried to fill this gap and have suggested simple strategies for preparing water-proof, lightweight, thin, and flexible shielding materials with high- performance EMI shielding in X, Ku, and K-band. Here, carbon nanofibers (CNF) were produced from electrospun PAN by carbonization at 900°C. The obtained CNF mats have inherent nitrogen doping with graphitic structure and 1-D fibrous, porous, and layer-by- layer structure which make them capable of absorbing EM waves. In the first approach, CNF was coated with poly(3,4-ethylenedioxythiophene): polystyrene sulfonate (PEDOT: PSS) with the assistance of polyvinylpyrrolidone (PVP) to improve the EMI shielding properties. Then, we explored different types of fillers such as inorganic semiconductor tellurium nanoparticles (NPs), Semiconductor metal oxide Nb2O5 NPs, conducting perovskite metal oxide La0.85Sr0.15CoO3 NPs, BaTiO3 NPs, and carbon black NPs, incorporated with CNF to improve the electric conductivity as well as EMI shielding properties. The flexible and hydrophobic polydimethylsiloxane (PDMS) composite of these samples have potential applications in flexible electronic devices as shielding materials for next-generation applications. PDMS allows us to design any type of complex structure, which make it suitable shielding materials for practical applications in different forms such as enclosure, gasket, coating over electronic circuits, and wrapping the electronic components.