A systematic study of titanium dioxide (TiO2) nanotubes (NTs) grown by electrochemical anodization in NH4F +glycerol electrolyte has been carried out in a broad range of anodization voltage of 5-350V and acid concentration of 0.1-0.7wt%. It is found that NTs can be grown in the voltage range from 10 to 240V. The maximum NH4F acid concentration at which NTs can be formed decreases with the anodization voltage (Va). The maximum NH4F acid concentration is 0.7% for Va<60V, and it decreases to 0.1% at Va = 240V. Glancing angle x-ray diffractometer (GAXRD) measurements show that as-grown amorphous TiO2 transforms to the anatase phase when annealed at 400 °C, and further transforms to the rutile phase at annealing temperatures higher than 500 °C. The transition temperature from anatase to rutile phase depends on the anodization conditions. The electrical resistivity of the NT increases by eight orders of magnitude when Va increases from 10 to 240V.