In this work, novel core-shell structured Fe3O4@NiS nanocomposites with different NiS: Fe3O4 mass ratios, namely x wt.% Fe3O4@NiS, have been successfully synthesized by a modified sedimentation-oxygenation method, in which the NiS outer layer (∼4nm) in-situ grown on the surface of Fe3O4 nanoparticles (∼30nm). For comparison propose, pure Fe3O4 as well as NiS ex-situ modified Fe3O4 composites (x wt.% Fe3O4/NiS) are also prepared and studied. When evaluated the electrochemical properties as anode material, all of the Fe3O4@NiS nanocomposites exhibit much better performance than pristine Fe3O4 material, due to the inhibition effect of NiS layer for retarding the generation of Fe(OH)2 passivation layer, which inevitably generates in the discharge process of the electrode and will hinder the OH− getting deeper into the active particles for further electrochemical reactions. Contrast to Fe3O4/NiS, Fe3O4@NiS nanocomposites also display better electrochemical properties owing to their relatively completer and more uniform NiS coating layer. In view of the advantages of the designed in-situ nano core-shell structure as the facile controlled synthesis process and low cost of the raw materials, it is believed the environment-friendly and high-performance Fe3O4@NiS nanocomposite is a promising type of anode candidate material for iron-based alkaline rechargeable batteries.