Monodispersed porous crystalline TiO2, SrTiO3, and BaTiO3 spheres were produced through a one-step hydrothermal process from amorphous TiO2 spheres. The resulting samples were characterized by scanning electron microscopy ( SEM), transmission electron microscopy ( TEM), X-ray diffraction ( XRD), and nitrogen sorption measurements. On the basis of the characterization results, we proposed a formation process of these porous spheres according to a mechanism analogous to the Kirkendall effect. This study provides a general way to synthesize porous titania-based spheres.