Ultrathin two-dimensional (2D) cobalt-organic framework (Co-MOF) nanosheets (NS) [Co-2(OH)(2)BDC, BDC = 1,4-benzenedicarboxylate] are prepared by a facile surfactant-assisted one-pot hydrothermal synthesis. The obtained ultrathin 2D Co-MOF NS are extremely thin, which contributes to their excellent electrical properties and optical transparency. These unique nanostructures make them good candidates as electrode materials for high-performance supercapacitors in terms of enhanced capacitance and stability. In a three-electrode system, ultrathin 2D Co-MOF NS have a maximum specific capacitance of 1159 F g(-1) at a current density of 0.5 A g(-1). More importantly, the as-prepared electrode exhibits very little capacitance decay after 6000 cycles with 96.7% retention of its original specific capacitance. Meanwhile, the ultrathin 2D Co-MOF NS electrode also offers superior performance in aqueous devices, is better than that of many other metal oxide-based electrodes. We believe that this material sheds light on exploring inexpensive and effective electrodes for high-performance supercapacitors.