The directional solidification and interface structure of Fe3O4-Y3Fe5O12 (yttrium iron garnet, YIG) eutectic grown in flowing air were investigated. The microstructure of the eutectic consisted of grains of broken and deformed lamellae. The orientation relationship between Fe3O4 and YIG is (011) Fe3O4 parallel to(513) YIG, (111) Fe3O4 parallel to(211) YIG and (211) Fe3O4 parallel to(311) YIG. The two phases of the eutectic showed the same orientation relationship mentioned above, even when the growth rates were changed from 5-90 mm h(-1). High-resolution TEM revealed that a disorder of the garnet structure of YIG occurs along the interface with a width of two or three atomic layers.