Single-crystal-like mesoporous strontium titanate (SrTiO3) submicrometer spheres with a wormhole-like structure were successfully synthesized by a facile hydrothermal method using polyvinyl alcohol (PVA) as additive. The microstructure was studied by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, high-resolution transmission electron microscopy, selected area electron diffraction, and N-2-physisorption techniques. The results demonstrated that the average pore size of the as-synthesized SrTiO3 mesoporous spheres can be tuned in the range of 4.5-16.1 nm by varying reaction time and adding PVA of different concentrations. The mesopores structure of the sample synthesized without PVA was different from that of the sample synthesized with PVA. For the former, the pores were contained in single-crystal particles in the presence of thick pore wall; in contrast, for the latter the pores occurred as voids between primary nanoparticles. On the basis of the investigation on the growth process, oriented aggregation of nanocrystallites was suggested to be the dominant growth mechanism, which was accompanied by the ripening process to form the high-quality mesoporous spheres. The photocatalytic activities of series samples were investigated through the degradation of rhodamine-B under exposure to the ultraviolet radiation (lambda=200-400 nm). The results indicated that the photocatalytic activities were the function of the reaction time and PVA concentration, Because both of them played an important role in the crystallinity, pore structure, and adsorption capacity in dark of the as-synthesized mesoporous SrTiO3 spheres.