H-trititanate nanotubes obtained by alkali hydrothermal treatment of TiO₂ followed by proton exchange were compared to their bulk H₂Ti₃O₇ counterpart with respect to their thermally induced structural transformation paths. As-synthesized and heat-treated samples were characterized by XRD, TEM/SAED, DSC and spectroscopy techniques, indicating that H₂Ti₃O₇ nanotubes showed the same sequence of structural transformations as their bulk counterpart obtained by conventional solid state reaction. Nanostructured H₂Ti₃O₇ converts into TiO₂(B) via multistep transformation without losing its nanotubular morphology. The transformation occurs between 120 and 400 °C through topotactic mechanisms with the intermediate formation of nanostructured H₂Ti₆O₁₃ and H₂Ti₁₂O₂₅, which are more condensed layered titanates eventually rearranging to TiO₂(B). Our results suggest that the intermediate tunnel structure H₂Ti₁₂O₂₅ is the final layered intermediate phase, on which TiO₂(B) nucleates and grows. The conversion of nanostructured TiO₂(B) into anatase is completed at a much lower temperature than its bulk counterpart and is accompanied by loss of the nanotubular morphology.