In this work, we report a very simple method to in situ prepare the Fe1−x Ni x (x =0, 0.3, 0.4, 0.5, 0.7 and 1) nano-alloys as the catalysts for H2 generation from the aqueous NH3BH3 solution under ambient atmosphere at room temperature. The prepared nano-alloys possess Pt-like high catalytic activity, especially for the specimen of Fe0.5Ni0.5, with which the hydrolysis of NH3BH3 would totally complete in only 2.2min. Moreover, these catalysts can be easily magnetically separated for recycle purpose, and can almost keep the same high activity even after 5 times of recycle under ambient atmosphere. Such alloy catalysts are expected to be useful for fuel cells, metal–air batteries and electrochemical sensors. Moreover, the concepts behind these preliminary results present a wide range of possibilities for the further development of synthesis of air and water-stable magnetic nano-alloys.