In this work Ni nanowires embedded in 18 cm2 anodic aluminium oxide templates were synthesized by electrodeposition to develop microwave absorbing materials. The complex permittivity and permeability properties of the Ni nanowires composite have been measured in the frequency range of 2–18 GHz. The resonance peak appeared at around 10 GHz in the permeability spectra. We found that the skin effect was suppressed in the composite, so the resonance peak was the consequence of the natural resonance resulting from the resonance absorption of the spin relaxation of magnetic moment in the Ni nanowires. The permeability spectra were fitted with the Landau–Lifshitz equation and the resonance frequency was calculated by the Kittel formula. Our calculation results agree well with the experimental data. The maximum reflection loss of the Ni nanowires composite with a thickness of 3 mm can reach 8.5 dB at 10 GHz, which shows promising application of the electrodeposited Ni nanowires composites in microwave absorbing area.