A new approach for the fabrication of periodic crystalline iron‐garnet thin films is introduced. Crystalline iron‐garnet planar triangular‐disposed thin film arrays are fabricated on SGGG substrate based on a selective‐area growth process, consisting of electron‐beam lithography patterning, soft ion‐milling, selective‐epitaxy, and chemical etching. Aluminum thin film is utilized in the processing, acting as a conductive layer to overcome any charge build‐up problem for the dielectric substrate. X‐ray diffraction results confirm that a crystalline iron‐garnet film can be deposited on a soft ion‐bombarded (GdCa)3(GaMgZr)5O12 (SGGG) surface by radio frequency (RF) plasma double ion‐beam sputtering. Planar periodic triangular‐disposed films are observed from field emission scanning electron microscope and atom force microscope, with diameters of 200–300 nm, a height of 30 nm, and a spacing interval of 350 nm. A typical hysteresis loop of magnetic materials is obtained. All results show this structure has great potential to be used as two‐dimensional magnetic photonic crystals (2D‐MPCs) and the selectively growth method can also be used to fabricate other 2D‐MPCs.