Ultrathin cobalt phosphate (CoHPO4$3H2O) nanosheets are successfully synthesized by a one pot hydrothermal method. Novel CoHPO4$3H2O ultrathin nanosheets are assembled for constructing the electrodes of supercapacitors. Benefiting from the nanostructures,the as-prepared electrode shows a specific capacitance of 413 F g1, and no obvious decay even after 3000 charge–discharge cycles. Such a quasi-two-dimensional material is a new kind of
supercapacitor electrode material with high performance.