Octahedron-shaped CoS2 crystals have been successfully fabricated through a simple hydrothermal route without any surfactant or template. The well-defined octahedral structures are highly uniform with a mean edge length of ∼ 360nm and exhibit a high geometric symmetry. The mechanism for the evolution process of the final octahedral structures is researched and proposed to begin with a growth and self-aggregation process, followed by an Ostwald ripening process. When electrochemically investigated as electrode materials for supercapacitors, the as-fabricated CoS2 electrode shows typical pseudocapative properties with a specific capacitance of 236.5 F g−1 at 1 A g−1. Remarkably, it exhibits an excellent cycling stability at 2 A g−1 with only a loss of 7.4% in the specific capacitance after 2000 cycles.