It is highly attractive but challenging to develop transition-metal electrocatalysts for direct hydrazine fuel cells (DHzFCs). In this work, a nickel crystalline core@nickel phosphide amorphous shell heterostructured electrocatalyst supported by active carbon (Ni@NiP/C) is developed. Ni@NiP/C with a P/Ni molar ratio of 3:100, Ni@NiP3.0/C, exhibits outstanding catalytic activity for the hydrazine oxidation reaction (HzOR) in alkaline solution, achieving a much better catalytic activity (2675.1 A gNifirstname.lastname@example.org V vs RHE) and high stability, as compared to Ni nanoparticles supported on carbon (Ni/C) and Pt/C catalysts. The results indicate that formation of the NiP amorphous shell effectively inhibits the passivation of the Ni core active sites and enhances the adsorption of hydrazine on Ni by improving the adsorption energy, leading to high electrochemical activity and stability of the Ni@NiP3.0/C catalysts for HzOR. The density functional theory calculation confirms the structural and electrocatalytic effect of the core-shell heterostructure on the stability and activity of Ni active sites for HzOR. The unique crystalline core/amorphous shell-structured Ni@NiP/C demonstrates promising potential as an effective electrocatalyst for DHzFCs.