Abstarct: With the advancements in modern technologies in fields such as equipment concealment, radio communications, and radar monitoring, serious issues have arisen, including wave interference, wave overlap, increased electromagnetic pollution, and the need for concealing equipment across different frequencies. These problems can lead to reduced efficiency of electronic, radio, and radar devices, potentially revealing equipment and threatening information security. One solution to tackle these issues is the use of electromagnetic wave-absorbing materials. Electromagnetic wave-absorbing materials can absorb and reduce the reflection and backscattering of radar waves in specific frequency ranges, thereby enhancing information security and equipment concealment. This research focuses on the fabrication and evaluation of (ZnxNix-1Fe2O4)/activated carbon nanocomposites produced from sisal biomass carbonization as electromagnetic wave-absorbing materials. Various techniques and analyses such as XRD, VSM, BET, FT-IR, VNA, and FESEM were employed to investigate and measure the characteristics and properties of the samples. Phase studies revealed that nickel-zinc nano-ferrites with different molar ratios of zinc ions were successfully synthesized, with the (Zn0.3Ni0.7Fe2O4) sample exhibiting the optimal composition of the constituent phases. Electron microscopy images confirmed the proper distribution of nickel-zinc ferrite nanoparticles and activated carbon produced from sisal biomass carbonization, with porous and dendritic structures. Using the FT-IR technique, functional groups present in the nanocomposites of (ZnxNix-1Fe2O4)/activated carbon produced from sisal biomass carbonization were identified. Additionally, in the measurement of magnetic properties, it was observed that the saturation magnetization changes and coercivity decreases with the increase in the molar ratio of zinc in the samples. In the investigation of microwave absorption properties within the frequency range of X band (2.8 - 12.4 GHz), the maximum reflection loss of -5.24 dB was recorded at a frequency of 10.82 GHz for the nanocomposite sample (Zn0.3Ni0.7Fe2O4)/activated carbon derived from biomass with a thickness of 2.5 mm. The reflection loss region for this sample was within the range of -10 dB to -94.16 dB, and the effective absorption bandwidth covered 8.53 GHz to 9.97 GHz in the X-band. Furthermore, microwave absorption properties were evaluated for sample thicknesses of 1.5 mm, 2.5 mm, 3.5 mm, and 4.5 mm for the nanocomposite (Zn0.3Ni0.7Fe2O4)/activated carbon derived from biomass. The sample with a thickness of 4.5 mm achieved a maximum reflection loss of -32.50 dB at 10.50 GHz and had an effective absorption bandwidth from 8.11 GHz to 11.54 GHz in the X-band.