A growth‐induced noncubic magnetic anisotropy, similar to that reported for garnets containing a mixture of rare earth ions, has been observed in YIG. It is illustrated by a comparison of X‐ray topographs of the crystal strain with the magnetic domain structure detected optically by means of the local Faraday rotation. Annealing at 1190°C in a nitrogen atmosphere removes the noncubic magnetic anisotropy. The suggested mechanisms involving a pairing or site preference of two or more different magnetic ions are not applicable to these results.