(Fe 1−x Co x ) 85 Si 9.6 Al 5.4 (wt.%) (x=0, 0.05, 0.10, 0.15, 0.20) nanocrystalline flakes have been prepared by high-energy planetary ball milling method from melt-spun ribbons. The as-milled powders were annealed at various temperatures ranging from 573 to 973K for 30min under the protection of nitrogen. XRD, SEM and VSM were used to characterize the microstructure and magnetic properties of the nanocrystalline powder samples. It was found that D0 3 superlattice phase was detected in the melt-spun ribbons, coexisting with α-Fe(Co) matrix phase. As the milling time reached 20h or longer, the D0 3 superlattice structure of Co-doped samples disappeared. When the milling time was prolonged to 70h, thin flakes with aspect ratio higher than 10:1 were achieved, and the corresponding average grain size was about 10nm. After 30min heat treatment, the D0 3 superlattice reappeared in the ball milled flakes when the annealing temperature was higher than 773K. In addition, heat treatment has an evident effect on internal stress relief. The saturation magnetization M s of Co-doped samples is larger than Co free samples. Moreover, the substitution of Co for Fe is beneficial to increase the Curie temperature (T C ) of nanocrystalline D0 3 phase from 733K for x=0 to 1000K for x=0.20, indicating a potential application in elevated temperatures.