Metalloborophene, characterized by the presence of metal‐centered boron wheels denoted as M©Bn, has garnered considerable attention in recent years due to its versatile properties and potential applications in fields such as electronics, spintronics, and catalysis. However, the experimental verification of metalloborophene is challenging, mainly due to the unconventional 2D boron networks. In this study, scanning tunneling microscopy, X‐ray photoelectron spectroscopy, low energy electron diffraction, and first‐principles calculations are employed to unveil Cu©B8 metalloborophene nanoribbons formed via spontaneous alloying after the deposition of boron on a heated Cu(110) substrate under ultrahigh vacuum condition. The thermodynamically preferred precursor, the anchoring of boron network to metal atoms, and anisotropic lattice mismatch are identified as pivotal factors in the formation of these metalloborophene nanoribbons. This discovery expands the repertoire of 2D materials and offers a potential pathway for the synthesis of other metalloborophenes. Metalloborophene nanoribbons characterized by the metal‐centered boron wheels (M©B8) are synthesized by depositing boron onto a copper surface under ultrahigh vacuum conditions. Scanning tunneling microscopy, X‐ray photoelectron spectroscopy and first‐principles calculations reveal several crucial factors contributing to the formation of this unexpected 2D material that hold promise for tailoring various properties such as catalysis and magnetism.