Magnetic chains self‐assembled from urchin‐like hierarchical Ni nanostructures have been successfully synthesized by a simple hydrothermal method requiring 4 h at 115 °C without any template or surfactant. The individual urchin‐like hierarchical nanostructures have an average diameter of 2–4 μm and are composed of well‐aligned sword‐like nanopetals growing radially from the surfaces of the spherical particles. The products were characterized by means of X‐ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy‐dispersive X‐ray spectroscopy analysis (EDX), Fourier transform infrared (FTIR) spectroscopy, thermogravimetric and differential scanning calorimetric analysis (TGA‐DSC). A rational formation mechanism of magnetic chains was proposed. Magnetic hysteresis measurements revealed that the as‐synthesized Ni chain‐like architectures display ferromagnetic behavior with saturation magnetization, remanent magnetization, and coercivity values of 52.58 emu/g, 5.82 emu/g, and 211.67 Oe, respectively.