In this work, attractive core–shell structured nanomaterials consisting of Ni doped Ag@C were synthesized. Further, a hydrogen peroxide (H₂O₂) sensor was fabricated by modifying the Ni doped Ag@C (Ni/Ag@C) nanocomposites onto the surface of a glassy carbon electrode (GCE). The composition and morphology of the Ni/Ag@C nanocomposites were characterized by scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy and Fourier transform infrared spectroscopy. The results indicated that the nanocomposites were synthesized successfully and showed similar grain sizes and favorable dispersity. The electrochemical and electrocatalytic properties of the Ni/Ag@C nanocomposites were studied by cyclic voltammetry. An electrochemical investigation showed that the Ni/Ag@C nanocomposite modified GCE exhibited a good electrocatalytic ability for H₂O₂ reduction and it was used for the determination of H₂O₂. The linear range for H₂O₂ determination was from 0.03 mM to 17.0 mM with a detection limit of 0.01 mM (S/N = 3). The sensitivity was 22.94 μA mM⁻¹ cm⁻². It is expected that the application of the Ni/Ag@C nanocomposites could be extended to the construction of other sensors and applications in various sensing fields.