The electromagnetic wave absorption properties of a magnetic powder with a fine α-Fe structure, produced by the disproportionation of Sm2Fe17, were investigated in the GHz frequency range. A fine, sub-micrometre α-Fe/SmH2 structure was formed from the Sm2Fe17 compound after disproportionation in a hydrogen atmosphere. The grain size of the α-Fe phase was calculated by X-ray diffraction line broadening analysis, to be about 30 nm. In this way, a magnetic powder with a fine structure of α-Fe was obtained. This powder was then heated in air in order to oxidize the SmH2, with the result that an α-Fe/SmO two-phase microstructure was obtained. Toroidally shaped epoxy-resin composites were made from this powder, and the microwave absorption properties of these samples were measured. As a result, the disproportionated samples (heated in hydrogen at 873 K for 1 hour, milled for 30 minutes and oxidized at 473 K for 2 hours in the air) exhibited electromagnetic wave absorption (R.L.<-20 dB) in the frequency range 0.75 to 1.3GHz, for absorber thicknesses ranging from 12.5 to 7.5 mm, respectively. An undisproportionated sample did not show any electromagnetic wave absorption in this frequency range.