The direct electroplating of Fe-Ni alloy films onto (100) n-type Si substrates were conducted. The electrodeposition phases, the film structure and the performance were investigated. The results show that when the current density is above 1.0 A/dm2, continuous films are formed and show an anomalous co-deposition progress occurs. When films are prepared with the current density from 1.0 to 4.0 A/dm2 the nickel composition can be adjusted from 45% to 78% (mass fraction), and the corresponding current efficiencies are from about 60% to 66%. The films consisting of 10~30 nm nanocrystallites show the fcc structure of solid solution of Fe-Ni. The magnetic hystersis loops of the alloy films exhibit a higher saturation magnetization and a very low coercive filed approaching zero, indicating that nanosized alloy films have very good soft magnetic performance.