A novel one-step and template-free preparation process had been developed to synthesize TiO2 hierarchically porous hollow spheres (HPHSs) by mixed solvents assisted flame spray pyrolysis (FSP). The as-obtained TiO2 HPHSs had hierarchically porous hollow structure such as central cavities, macropores on shells, and mesopores accumulated by TiO2 nanocrystallites. The unique hierarchically porous structure endowed the TiO2 spheres with high specific surface area and excellent light scattering property. A mechanism of the formation of TiO2 HPHSs depending on the competition between chemical reaction rate and diffusion rate of the components of the precursor was proposed, in which mixed solvents and short flame residence time were of importance. Furthermore, the dye-sensitized solar cells (DSSCs) performance of TiO2 HPHSs as light scattering layer was investigated. The photoelectric conversion efficiency (eta) was improved by 38.2% (from 5.00% to 6.91%), comparing to that of single layer P25 films.