Constructing unique mesoporous 2D Si nanostructures to shorten the lithium‐ion diffusion pathway, facilitate interfacial charge transfer, and enlarge the electrode–electrolyte interface offers exciting opportunities in future high‐performance lithium‐ion batteries. However, simultaneous realization of 2D and mesoporous structures for Si material is quite difficult due to its non‐van der Waals structure. Here, the coexistence of both mesoporous and 2D ultrathin nanosheets in the Si anodes and considerably high surface area (381.6 m2 g−1) are successfully achieved by a scalable and cost‐efficient method. After being encapsulated with the homogeneous carbon layer, the Si/C nanocomposite anodes achieve outstanding reversible capacity, high cycle stability, and excellent rate capability. In particular, the reversible capacity reaches 1072.2 mA h g−1 at 4 A g−1 even after 500 cycles. The obvious enhancements can be attributed to the synergistic effect between the unique 2D mesoporous nanostructure and carbon capsulation. Furthermore, full‐cell evaluations indicate that the unique Si/C nanostructures have a great potential in the next‐generation lithium‐ion battery. These findings not only greatly improve the electrochemical performances of Si anode, but also shine some light on designing the unique nanomaterials for various energy devices. Ultrathin mesoporous 2D Si nanosheets with enhanced electrochemical performance are successfully developed by a scalable and low‐cost method. After being encapsulated with the homogeneous carbon layer, the Si/C nanocomposite anodes achieve outstanding lithium‐storage properties with good rate capacity and remarkable cycling stability, which illustrates that the unique nanomaterial is a promising candidate material for the next‐generation lithium‐ion batteries.