The structures of a water atomized and a mechanically milled FeSi2 powder were studied with X-ray diffraction, scanning electron microscope and Fe-57 Mossbauer spectroscopy. X-ray diffraction pattern showed that a water atomized powder was constitued of alpha-FeSi2, and epsilon-FeSi. The solidification structure like a dendrite was observed at the surface and the inside of their particles. And this powder changed to the nanostructured beta-FeSi2, by mechanical milling without a thermal treatment. Fe-57 Mossbauer spectrum for a atomized powder was fitted with three paramagnetic doublets corresponded to alpha-FeSi2 and epsilon-FeSi. The spectrum for a mechanically milled atomized powder was fitted with two doublets of beta-FeSi2.