This study introduces ZnFe2O4@MWCNTs nanocomposites (ZF@MWCNTs NCs), developed using ZnFe2O4 magnetic nanoparticles (ZFNPs) and multi-walled carbon nanotubes (MWCNTs) via a simple, cost-effective, and scalable ultrasonic process. The design involves ZFNPs acting as an electromagnetic (EM) skeleton or magnetic shell surrounding a conductive MWCNT core, optimizing microwave absorption. By combining the magnetic properties of ZFNPs and the electrical conductivity of MWCNTs, the quasi-core-shell structure achieves excellent impedance matching and synergistic dielectric/magnetic loss. Comprehensive characterization was performed, including X-ray diffraction (XRD) for crystal structure, field emission scanning electron microscopy (FESEM) with energy-dispersive X-ray spectroscopy (EDS) for morphology and elemental analysis, Fourier transform infrared (FT-IR) spectroscopy for structural identification, vibrating sample magnetometers (VSM) for magnetic properties, and vector network analyzers (VNA) for dielectric properties. Among the five synthesized weight ratios, M4 sample exhibited the best reflection loss (RL) under the X-band at −47.16 dB with a thickness of 2.33 mm and under the Ku-band at −24.40 dB with a thickness of 1.53 mm. These nanocomposites demonstrated 99.99 % wave dissipation under both X- and Ku-bands, making them highly effective microwave absorbers. This work provides a promising approach for developing high-performance microwave-absorbing materials.