Abstract Fe nanostructures with different morphologies were synthesized by the borohydride reduction method without any surfactants. Through simply controlling the reaction temperature, spherical and wire-like iron nanoparticles were obtained, and their crystal phases and morphologies were characterized. The electromagnetic characteristics and microwave absorption properties of Fe nanostructures were investigated. Compared with the Fe nanospheres, the permeability and permittivity of the Fe nanowires were increased dramatically and the ferromagnetic resonance frequency shifts to higher frequency, leading to an amazing enhancement of microwave absorption property. For the Fe nanowires, an optimal reflection loss of −32dB was obtained at 1.3GHz with a thinner matching thickness of 3.5mm and reflection loss exceeding −10dB were observed in the 0.8–2.1GHz range for 2–4mm thickness. This result suggests that the Fe nanowires can be used as a potential microwave-absorbing material at quasimicrowave band (L-band) owing to its excellent microwave properties.