Rational structure and morphology design are of great significance to realize excellent Na storage for advanced electrode materials in sodium‐ion batteries (SIBs). Herein, a cube‐like core/shell composite of single MnS nanocubes (≈50 nm) encapsulated in N, S co‐doped carbon (MnS@NSC) with strong CSMn bond interactions is successfully prepared as outstanding anode material for SIBs. The carbon shell significantly restricts the expansion of the MnS volume in successive sodiation/desodiation processes, as demonstrated by in situ transmission electron microscopy (TEM) of one single MnS@NSC nanocube. Moreover, the in situ generated CSMn bonds between the MnS core and carbon shell play a significant role in improving the Na‐storage stability and reversibility of MnS@NSC, as revealed by in situ Raman and TEM. As a result, MnS@NSC exhibits a high reversible specific capacity of 594.2 mAh g−1 at a current density of 100 mA g−1 and an excellent rate performance. It also achieves a remarkable cycling stability of 329.1 mAh g−1 after 3000 charge/discharge cycles at 1 A g−1 corresponding to a low capacity attenuation rate of 0.0068% per cycle, which is superior to that of pristine MnS and most of the reported Mn‐based anode materials in SIBs. A cube‐like core/shell composite of single MnS nanocubes encapsulated in N, S co‐doped carbon (MnS@NSC) with strong CSMn bond interactions is prepared successfully. As demonstrated by electrochemical tests and in situ studies, the MnS@NSC delivers high reversible capacity, excellent cycling stability, and rate capability as anode material in sodium‐ion batteries, which benefits from the sulfur‐bridged bonds and unique core/shell structure.