Ni‐Co alloy is worth notice as a material for fabricating a magnetoresistance element, because of the highest magnetoresistance anisotropy (&Dgr;&rgr;/&rgr;0) in the ferromagnetic alloys. We studied the magnetoresistance anisotropy and the crystal structure on the films of the Ni‐Co alloy system (40 Ni–60Co∼81Ni–19Co). In this study we found the following facts: (1) A new ordered phase exists in the films around at the composition 50Ni–50Co prepared at a substrate temperature above about 550 °K. (2) This ordered phase is accompanied with a newly proposed superstructure. (3) A close relation exists between the magnetoresistance anisotropy and the degree of order, and the films in the ordered state have a higher anisotropy ratio (&Dgr;&rgr;/&rgr;0) than the bulk value. This fact is important in the practical application, such as a magnetic field sensor.