This paper presents a facile hydrothermal route to synthesize monodispersive and single-crystalline BaHfO3 hollow micro- and nanospheres in a concentrated basic environment. The hollow spheres were size tunable from submicrometer to nanoscale by simply adjusting the base concentration at a suitable temperature. The base concentration played the key role on forming BaHfO3 hollow spheres. Detailed investigations on base concentration, reaction temperature, and duration indicated that the formation of BaHfO3 hollow spheres was driven by Ostwald ripening process. Because of the abundance of defects, the as-prepared BaHfO3 hollow nanospheres exhibited a blue light emission under UV-light excitation at room temperature. Calcination led to the photoluminescence declination due to the decrease of defects.