An Fe-50at %Ni alloy was processed by high-pressure torsion (HPT) and annealed at lower homologous temperatures. Vickers microhardness and microstructural evolutions were examined with respect to the annealing time. Disks with 10 mm diameters having 0.85 mm thicknesses were subjected to HPT under a pressure of 6 GPa for 1-10 revolutions at a rotation speed of 1 rpm. The annealing after the HPT processing was conducted at homologous temperatures of ~0.3 for up to 40 days. The hardness increases with straining and saturates to a constant level of ~400 Hv at large equivalent strain. Microstructure analysis using XRD revealed that there was a peak corresponding to an α (Fe, Ni) phase.