Mesoporous anatase TiO2 spheres with tunable sizes ranging from 400 nm to 3 μm were synthesized using an original so-called "water-controlled solvothemal release process". In this method, the well-known esterification reaction between ethanol and acetic acid was creatively employed to generate water gradually during a solvothermal process. Thereafter, the slowly released water molecules functioned as nucleation centers for completing the hydrolysis of titanium tetraisopropoxide to produce homogenous mesoporous TiO2 spheres. In reality, these samples consisted of densely packed nanoparticles that formed spherical secondary particles with interparticle pores. Research has demonstrated that the diameter of the TiO2 spheres can be easily tuned by controlling the concentration of the Ti source in the starting solution. Regardless of their diameter, all of these TiO2 spheres exhibited a high specific surface area (above 150 m2 g-1) originating largely from the contribution of mesopores. On the merits of their porous structure and related high specific surface area, the mesoporous TiO2 spheres showed a higher photocatalytic activity than P25 for the oxidative photo-destruction of NOx gas.