The anisotropy constant Ku and the intrinsic coercive force MHc were determined in the temperature range 4.2° to 297°K on a single crystal of Co 3.5 Fe .5 CuCe 1.09 . Also, a magnetization curve was obtained on a thermally demagnetized sample of this composition in which domain walls were present. It was necessary for the applied field to reach the value of the coercive force to substantially change the magnetization. As a result of these magnetic measurements and the direct observation of the precipitate particles by Leamy and Green using transmission electron microscopy, it appears that the magnetization process is governed by domain wall pinning.