An efficient BaAlxFe12−xO19- novolac phenolic resin (NPR) nanocomposite material is developed to use as absorbing material in the X band. The material developed has a hexagonal structure of nanosize aluminium substituted barium ferrite, as is confirmed by X-ray diffraction pattern studies. The average grain size of barium nanoparticles is found to be ~26 nm. Measurement of complex permittivity and complex permeability in the X-band indicates increase of the properties with increase in Al3+ ions in the ferrite. A measured absorption study has been carried out on absorber fabricated on a metal backing based on the transmission line theory. Substitution of Fe3+ with Al3+ is found to increase the absorption properties of barium ferrite. Reflection loss measurement of the samples shows an enhancement of absorption from −27.56 dB to −40.06 dB with the variation of Al3+ substitution, x=1.0–1.6 in the BaAlxFe12−xO19 in NPR matrix.