MOF/inorganic nanocomposites combine the advantages of each component. Herein, two MOF/metal selenite nanocomposites, Co-NH 2 -BDC/CoSeO 3 ·H 2 O and Co-BDC/CoSeO 3 ·H 2 O, are prepared on nickel foam through a facile two-step hydrothermal method, which inherit the 2D morphology and porosity properties of their MOF precursors. Furthermore, during the electrochemical activation process, the crystallized nanocomposites can easily transform into amorphous structures in a short time of 20 min in the presence of an electric field, similar to CoSeO 3 ·H 2 O. Due to amorphization, the electrochemical performance of the two nanocomposites is much enhanced relative to that of their MOF precursors. Specifically, the areal capacitances of Co-NH 2 -BDC/CoSeO 3 ·H 2 O and Co-BDC/CoSeO 3 ·H 2 O are 5.35 and 10.65 F·cm -2 at 2 mA·cm -2 , respectively. The assembled asymmetric supercapacitor (ASC) using Co-NH 2 -BDC/CoSeO 3 ·H 2 O as positive electrodes delivers an energy density of 0.207 mWh·cm -2 at a power density of 0.799 mW·cm -2 with outstanding cycling stability (93% capacity retention after 5000 cycles). Using Co-BDC/CoSeO 3 ·H 2 O as positive electrodes, the ASC can reach a high energy density of 0.483 mWh·cm -2 at a power density of 0.741 mW·cm -2 and 84% capacity retention after 5000 cycles. This work provides an efficient strategy for constructing MOF/metal selenite nanocomposites for energy storage and conversion.