Transition metal nitrides are promising alternative anode materials for the next-generation high-energy and high-power lithium ion batteries because of their large specific capacity and superior electronic and ionic conductivity. In this work, nanocrystalline γ″-FeN thin films are prepared by reactive magnetron sputtering and their lithium-storage performance is investigated. The γ″-FeN electrode retains high specific capacities of 1020.4 mAh/g after 100 discharge/charge cycles at the current density of 0.2 A/g and 667.1 mAh/g after 500 cycles at 2 A/g. Even at 10 A/g, a remarkable specific capacity of 469.0 mAh/g is achieved. Scanning and transmission electron microscopic analyses both prove that the microstructure of γ″-FeN thin film is durable against repeated lithiation and delithiation reactions.