Fe nanowires with 70–200nm in diameter and 20–50μm in length were synthesized by a chemical vapor deposition method for electromagnetic wave absorption application. The frequency dependences of relative permittivity (εr) and permeability (μr) were strongly dependent on the diameter of Fe wires. Compared with micrometer wires or flakelike samples, nanowires exhibited a magnetic resonance (μr″) peak in the range of 1–18GHz, suggesting that nanowires have significant effect for reducing the eddy current loss, therefore, the resin compacts of 29vol% Fe nanowires with thicknesses of 1.3–4.0mm provided good electromagnetic wave absorption performances in the range of 5.6–18GHz.