Ever-increasing energy crises require the exploration of sustainable energy conversion and storage systems that are reliable, low-cost and environmentally friendly. The search for Earth-abundant and efficient electrode materials is significant for advanced supercapacitors. Transition metal chalcogenides has regarded as one of the most emerging new materials for electrochemical energy storage device. Manganese diselenide is a low-cost and eco-friendly semiconducting material with applications in lithium ion battery and oxygen reduction catalysis. However, there have been fewer reports on the electrochemical performance research of manganese diselenide. In this study, cubic manganese diselenide (MnSe₂) were synthesized by using a one-pot hydrothermal method. Physicochemical characterizations revealed the formation mechanism of MnSe₂ nanosheets. Electrochemical analysis suggested the pseudocapacitive nature of MnSe₂ electrode, which delivered a specific capacitance of 423 F g^-1 at a current density of 1 A g^-1, and obtained 203 F g^-1 at 30 A g^-1. The superior electrochemical performance of MnSe₂ nanosheets highlights the potential use as electrode material in supercapacitor.