Co-Pt alloy film magnets were prepared by electrodeposition. After annealing as-deposited films with face-centered-cubic (fcc) crystal structure, the structure of films with 24 to 50 at.% Co content transformed from disordered fcc phase to ordered face-centered-tetragonal (fct) L10 phase. It was clarified that Co-Pt film magnets with a Co content of 43 at.% have high coercivity of approximately 880 kA/m. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 157(4): 7–12, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20216