Ferromagnetic gadolinium silicide (Gd5Si4) nanoparticles significantly enhance the microwave absorption bandwidth of a polymer blend (PVB-PEDOT:PSS). These materials are critically needed for various military and civilian applications such as X-band (8.2–12.4 GHz) and Ku-band (12.4–18 GHz) absorption. A single 1.2 mm thick layer of PVB-PEDOT:PSS-Gd5Si4 (PPGS) nanocomposite film shows the most promising bandwidth (8.2–18 GHz) with a minimum reflection loss of -14 dB. Mechanistically, dielectric loss (tan δ_e ≈2.4) and magnetic loss (tan δ_m ≈1.1) contributes more efficiently, and standard microwave simulation confirms the stored energy is predominant in PPGS nanocomposite which enhances the bandwidth.