Ball in cage structures of cobalt sulfide have been successfully prepared by a facile one-pot hydrothermal synthesis approach employing Co(NO3)2·6H2O as the cobalt source and S=C(NH2)2 as the sulfur source. The effects of the reaction parameters (volume ratio of distilled water to ethanol, reaction time and reaction temperature) on the morphology and size of the CoS structures were investigated. The synthesized product was characterized by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. It has been confirmed that the volume ratio of distilled water to ethanol played a key role in the formation of the ball in cage structures, and the formation mechanism of the CoS ball in cage structures was also proposed. The electrochemical capacitance performances of the CoS products were studied, and the CoS ball in cage structures show excellent energy storage characteristics. Ball in cage structures of cobalt sulfide have been successfully prepared by a facile one-pot hydrothermal synthesis approach approach Co (NO3) 2 .6H2O as the cobalt source and S = C (NH2) 2 as the sulfur source. The effects of the reaction parameters (volume ratio of distilled water to ethanol, reaction time and reaction temperature) on the morphology and size of the CoS structures were investigated. The synthesized product was characterized by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. It has been confirmed that the volume ratio of distilled water to ethanol played a key role in the formation of the ball in cage structures, and the formation mechanism of the CoS ball in cage structures was also proposed. The electrochemical capacitance performances of the CoS products were studied, and the CoS ball in cage structures show excellent energy storage characteristics.