FeNiN thin films with good soft magnetic properties were synthesized on Si (100) substrates at 473K by RF magnetron sputtering. The dependence of phase structure and magnetic properties on nitrogen partial pressure, nickel concentrations, film thickness and substrate temperature were systematically investigated. The phase evolution from α-(Fe,Ni)N to ξ-(Fe,Ni)2N with increase of nitrogen partial pressure was seen. The addition of Ni caused FeNiN films to turn from BCC structure to FCC structure. Clear reproducible striped domains appeared at the film surfaces when XNi=19.6%, which is explained by the high enough perpendicular anisotropy and the small stress in the film. All films show smooth surfaces and good soft magnetic properties compared to corresponding FeN compounds. The magnetic properties depended dramatically on the phase structure. Optimum soft magnetic properties with HC of