AbstractInspired by the significant advantages of the bottom‐up synthesis whose structures and functionalities can be customized by the selection of molecular components, a 2D metal‐organic framework (MOF) nanosheet Co‐BTB‐LB has been synthesized by a liquid–liquid interface‐assisted method. The as‐prepared Co‐BTB‐LB is identified by scanning electron microscopy/energy dispersive spectroscopy (SEM/EDX) and X‐ray photoelectron spectroscopy (XPS), and the sheet‐like structure is verified by scanning electron microscopy (SEM), high‐resolution transmission electron microscopy (HRTEM), and atomic force microscopy (AFM). Co‐BTB‐LB electrode exhibits an excellent capacity of 4969.3 F g−1at 1 A g−1and good cycling stability with 75% capacity retention after 1000 cycles. The asymmetric supercapacitor device with Co‐BTB‐LB as the positive electrode shows a maximum energy density of 150.2 Wh kg−1at a power density of 1619.2 W kg−1and good cycling stability with a capacitance retention of 97.1% after 10000 cycles. This represents a state‐of‐the‐art performance reported for asymmetric supercapacitor device using electroactive bottom‐up metal‐complex nanosheet, which will clearly lead to a significant expansion of the applicability of this type of 2D nanomaterials.