3D interconnected ultrathin CoSe nanosheets are prepared via a hydrothermal synthesis method and utilized as superior battery-like electrode material for the first time. Due to the features of the unique 3D interconnected ultrathin nanosheets with a large BET specific surface area, superior mesoporous structure and good electrical conductivity, the as-resulted 3D interconnected ultrathin CoSe nanosheets manifests a high specific capacity of 70.6 mAh g−1 at 1 A g−1 and remarkable rate performance with 52.8% of capacity retention rate at 100 A g−1 compared with 1 A g−1. Furthermore, a novel aqueous hybrid supercapacitor is assembled by employing 3D interconnected ultrathin CoSe nanosheets and activated carbon as the cathode and anode, respectively. The assembled hybrid device displays a specific energy of 18.6 Wh kg−1 at a specific power of 750 W kg−1 and outstanding cycling life with 95.4% of the initial capacity retention for 20000 cycles at 5 A g−1. These results imply that the unique 3D interconnected ultrathin CoSe nanosheets can be considered as highly potential candidate electrode materials for hybrid supercapacitors.