Herein, we developed a simple template-free synthetic method for producing niobium pentoxide (Nb2O5) hollow nanospheres, and fabricated KNbO3 hollow nanospheres which retained the morphology of the template Nb2O5 hollow nanospheres by the molten salt method. The formation of Nb2O5 hollow nanospheres was via Ostwald ripening, and the structural evolution between niobium oxide and niobates was a kind of self-sacrificing templated process. These Nb2O5 hollow nanospheres with high surface energy (001) planes showed high thermal stability and large surface area. Furthermore, they not only showed strong intensity of blue emission, but they were also able to efficiently split water under visible light irradiation, and show potential for application as sensors, optoelectronic devices and promising photocatalysts for water splitting under visible light. Due to the high thermal stability of Nb2O5 hollow nanospheres and the simplicity of the protocol, we anticipate that this work will enrich the hollow nanostructures of inorganic compounds and provide a new strategy to synthesize hollow nanospheres of niobates and other kinds of materials.