In this study, a novel B‐containing SiOx composite is demonstrated with a remarkably improved cycling performance as a stable anode material for lithium‐ion batteries. A multielement, multiphase, B‐containing SiOx composite is successfully prepared by heating a mixture of SiO and LiBH4 to 500 °C. The resultant product consists mainly of amorphous/nanocrystalline Si, SiOx, B, B2O3, and Li2SiO3. The in situ formed amorphous B, B2O3, and nanocrystalline Li2SiO3 mostly remain at the surface of the product particles, providing a remarkable enhancement in the mechanical properties of the Si/SiOx active materials. This feature provides good accommodation for the volume change during lithiation/delithiation, consequently depressing the pulverization and fracture of the Si/SiOx active materials. As a result, the cycling stability of the prepared B‐containing SiOx composite is significantly improved. The sample prepared from SiO–0.3LiBH4 delivers reversible capacity of 1186 mAh g−1 at 100 mA g−1 after 100 deep cycles, corresponding to the capacity retention of 81%. This outcome is more than two times higher than that of pristine SiO (33.9%).