We demonstrate a facile and controllable synthesis of horn-like Co3O4 nanostructures through a solvothermal process followed by calcination at different temperatures. The particle sizes and defects of the as-obtained Co3O4 nanohorns are controlled with respect to calcining temperatures, while preserving the horn-like morphology. In particular, the Co3O4 nanohorn electrodes prepared at 300 degrees C reveal the specific capacitance of similar to 2751 F g(-1) and the rate capability of 46.8%, which is greater than those of materials obtained at 350, 400, and 450 degrees C. In order to enlarge the potential window, a hybrid supercapacitor is configured with the Co3O4 nanohorn and activated carbon used as positive and negative electrodes, respectively. The as-fabricated hybrid supercapacitor shows high specific capacitance of similar to 101 F g(-1) and the rate capability of 80.5%. The energy and power densities of hybrid supercapacitor are similar to 31.70 W h kg(-1) and 16.71 kW kg(-1), respectively, along with 91.37% of capacitance retention over 350,000 cycles. These energy and power densities of the hybrid supercapacitors are approximately 8.5 and 3.5 times greater than values of Co3O4 symmetric supercapacitor.