The formation process of nitrogen doped mesoporous TiO2 spheres can be explained through the schematic illustration shown in Scheme 1. Firstly, TiO2 seed crystals grow into TiO2 nanoparticles in size of 12 nm, and then self-assemble together into TiO2 sphere precursor in the presence of PVP and CTAB. The PVP cannot only increase the Zeta potential of inter-particles repulsion, but also form a steric hindrance, which can reduce the contact between different reactive molecules and decrease the reaction rate. The decrease of nucleation and growth rate is beneficial for the for-mation of TiO2 sphere. Secondly, ammonia was added as nitrogensource and by way of hydrothermal treatment, ammonia woulduniformly diffuse from the surface to the bulk of TiO2sphere. Lastly,after calcination at 400◦C, the template CTAB was removed, producing worm-like pores. Nitrogen atom was introduced into thelattice of crystalline TiO2 nanocrystals which are assembled to asphere. The substitution N atoms are highly dispersed into the bulk of n-N-TiO2 sphere to achieve the homogeneous doping of N from the bulk to the surface of TiO2 sphere, which is expected to improve the visible light photocatalytic activity.