Size tunable perovskite-type BaZrO₃ hollow micro- and nanospheres have been hydrothermally synthesized in a strong basic medium without any organic or inorganic templates. The products experienced morphology variations of solid, core-shell and hollow nanospheres by alternatively adjusting the base concentration, the reaction temperature or the reaction duration. Investigations on the synthetic parameters revealed that the formation of BaZrO₃ hollow nanospheres was driven by the Ostwald ripening process. BaZrO₃ hollow nanospheres were produced when the reaction temperature and the base concentration were in a suitable rate due to their functions to elevate the crystal growth speed and the diffusion rate. XRD patterns disclosed the cubic perovskite structure of BaZrO₃ hollow spheres. HRTEM and SAED measurements revealed the single crystal nature of a single BaZrO₃ hollow nanosphere. The hollow spheres were size tunable by simply adjusting the base concentration at a suitable temperature, which was rationally elucidated by the sol–gel theory. The hollow nanospheres exhibited an intensive green light emission and excellent reactive dye adsorption.