Nanocomposites α-Fe/Fe3B/Y2O3 were prepared by a melt-spun technique, and the electromagnetic wave absorption properties were measured in the 0.05～20.05 GHz range. Compared with α-Fe/Y2O3 composites, the resonance frequency (fr) of α-Fe/Fe3B/Y2O3 shifted to a higher frequency range due to the large anisotropy field (HA) of tetragonal Fe3B (～0.4 mA·m-1). The relative permittivity (εr=εr′-jεr″) was constantly low over the 0.5～10 GHz region, which indicates that the composite powders have a high resistivity (ρ=～100 Ωm). The effective electromagnetic wave absorption (RL＜-20 dB) was obtained in a frequency range of 2.7～6.5 GHz on resin composites of 80% (mass fraction) α-Fe/Fe3B/Y2O3 powders, with thickness of 6～3 mm respectively. A minimum reflection loss of -33 dB was observed at 4.5 GHz with an absorber thickness of 4 mm.