Thermally stable mesoporous TiO2 spheres were successfully prepared via in situ hydrolysis of a titanium glycolate precursor. The mesoporous nature was retained even with calcination up to 500 degrees C under static air conditions. Mesoporous TiO2 calcined at 500 degrees C showed the maximum photocatalytic activity. This is mainly attributed to the better utilization of charge carriers due to the low diffusional length along with high surface area and well-defined nanocrystallinity.