In the current investigation, a modified process combining pre-annealing and post-hydrothermal treatments has been applied on the as-dried TiO 2 nanotubes derived from alkaline route of TiO2 P25 nanoparticles in 10 M NaOH solution. The combined treatment is purposely aimed at enhancing the nanocrystallinity of anatase TiO2, while at the same time maintaining the integrity of the nanotube hollow structures. The detail of the structure, morphology and crystallinity of the resulting nanotubes were examined by XRD, SEM and TEM, while the optical properties of nanotubes were investigated by UV-visible spectroscopy. For the nanotube samples which have been previously annealed at 300°C, the crystallite size of anatase TiO 2 in nanotubes increased from 17.20 to 18.30 nm after being subjected to post-hydrothermal treatment at 100 to 150°C. The band gap energy (E g) of the resulting nanotubes is inversely proportional to the crystallite size of anatase phase where the lowest value of 3.21 eV was obtained from the TiO2 nanotube sample with the biggest crystallite size of 18.30 nm.