A Co₉S₈ film was in-situ deposited onto nickel foam substrate via a hydrothermal electrochemical deposition method. The morphology, composition and structure of the as-prepared film were characterized and the electrochemical performances were tested. The result showed that the as-synthesized Co₉S₈ film displayed a petal-like morphology and possessed excellent capacitive behavior with a specific capacitance of 2538.7 F/g at a discharge current density of 10 mA/cm₂, and retained to 1930.7 F/g even at a higher density of 50 mA/cm₂. After 1000 cycles at 20 mA/cm₂, the specific capacitance of 1825.2 F/g still remained, and the capacitance retention is calculated to be 72.8%. Even after 1500 cycles, the specific capacitance retention could retain to 61.4%.