Hollow Co2P nanoflowers (Co2P HNFs) were successfully prepared via a one-step, template-free method. Microstructure analysis reveals that Co2P HNFs are assembled from nanorods and possess abundant mesopores and an amorphous carbon shell. Density functional theory calculations and electrochemical measurements demonstrate the high electrical conductivity of Co2P. Benefiting from the unique nanostructures, when employed as an electrode material for supercapacitors, Co2P HNFs exhibit a high specific capacitance, an outstanding rate capability, and an ultralong cycling stability. Furthermore, the constructed Co2P HNF//AC ASC exhibits a high energy density of 30.5 W h kg-1 at a power density of 850 W kg-1, along with a superior cycling performance (108.0% specific capacitance retained after 10 000 cycles at 5 A g-1). These impressive results make Co2P HNFs a promising candidate for supercapacitor applications.