This article reports on the relations between the magnetic properties and crystal structure of Co‐Fe‐Al‐N films prepared by rf magnetron sputtering in a mixed Ar and N2gas atmosphere. Slightly substrate‐biased 4 at. % Al films showed a low coercivity of less than 80 A/m, a low magnetostriction of less than 1×10−6, and a high saturation magnetic flux density of 1.7 T. These features were maintained after annealing at up to more than 500 °C. The lowHcwas related to the crystal structure of a face‐centered‐cubic phase with an about 10‐nm grain size. No detectable AlN was observed by an x‐ray diffractometry even after annealing. However, the lattice constant after annealing was nearly equal to that of a Co‐Fe alloy and the Al content increased with the increase in sputtering N2‐gas content, suggesting the binding of Al and N atoms.