Mesoporous TiO2 is attracting increasing interest due to properties suiting a broad range of photocatalytic applications. Here we report the facile synthesis of mesoporous crystalline TiO2-B nanobelts possessing a surface area as high as 80.9 m2 g���1 and uniformly-sized pores of 6���8 nm. Firstly, P25 powders are dissolved in NaOH solution under hydrothermal conditions, forming sodium titanate (Na2Ti3O7) intermediate precursor phase. Then, H2Ti3O7 is successfully obtained by ion exchange through acid washing from Na2Ti3O7 via an alkaline hydrothermal treatment. After calcination at 450 ��C, the H2Ti3O7 is converted to a TiO2-B phase. At 600 ��C, another anatase phase coexists with TiO2-B, which completely converts into anatase when annealed at 750 ��C. Mesoporous TiO2-B nanobelts obtained after annealing at 450 ��C are uniform with up to a few micrometers in length, 50���120 nm in width, and 5���15 nm in thickness. The resulting mesoporous TiO2-B nanobelts exhibit efficient H2 evolution capability, which is almost three times that of anatase TiO2 nanobelts.