The present invention provides a cerium-containing magnetic garnet single crystal having a size large enough to use as a material for optical communication of an isolator and for an electronic device, and a production method therefor. The cerium-containing magnetic garnet single crystal of the present invention is obtained by melting a cerium-containing magnetic garnet polycrystal while applying a sharp, large temperature gradient to the solid-liquid interface of the melt and the solid, and then solidifying the melted polycrystal. The polycrystal is preferably heated by using an optical heating device, for example, a combination of a main heating device using a laser beam, and an auxiliary heating device using reflected light from a halogen lamp.