The development of highly efficient catalysts towards ammonia decomposition is a promising strategy for COx-free hydrogen production. Herein, we synthesized an active catalyst using Ni nanoparticles (NPs) dispersed on MgO and N-doped carbon nanofiber (NCFs) (Ni/MgO@NCFs) catalyst by pyrolysis followed by hydrothermal method. The X-ray diffraction (XRD) and Raman analyses studied the crystal formation of the heterostructure, and HR-TEM results revealed that Ni NPs with 4.5 nm in size were uniformly embedded in the NCFs. As a result, the optimum Ni@MgO-NCFs (10 wt.%) exhibit superior catalytic performance and excellent stability activity for 60 h at 300 °C and 450 °C. This work promises to explore Ni@MgO-NCFs catalyst as a new kind of effective catalyst for ammonia decomposition and to enhance the catalytic activity by controlling the metal-support interaction of the catalysts.