Disclosed are a composition for an Fe-based alloy and an Fe-based amorphous alloy powder, whereby a high-purity amorphous structure is maintained even after coating by thermal spraying or the like, but also various physical properties are improved. The composition for the Fe-based alloy includes iron, chromium, and molybdenum, wherein per 100 parts by weight of the iron, the chromium is contained in an amount of 25.4 to 55.3 parts by weight, the molybdenum is contained in an amount of 35.6 to 84.2 parts by weight, and at least one of carbon and boron is further contained.