Abstract Nanocrystalline Fe x Ni 1− x alloys ( x = 0.15, 0.20, 0.22, 0.25, 0.30, 0.50 and 0.65) were produced by a wet chemical method. The metal concentration ratios in the solutions were preserved in the precipitated powder alloys and no metal segregation was detected. The FCC phase was observed from x = 0.15 to 0.50. For x = 0.65 both FCC and BCC phases were observed. The materials obtained consist of nanoparticles with a mean diameter of 90 nm. The latter are composed of several nanocrystallites surrounded by a low density structurally disordered region. The crystallite size in the FCC phase increased as the at.% Fe decreased from ∼10 nm for x = 0.50 to ∼20 nm for x = 0.15. A different thermal behavior was observed for the x = 0.50 in comparison to the x = 0.22 sample.