TiO2 nanostructures by the hydrothermal process can be potential materials in the various fields of application due to their inherent ion-exchange capabilities and unique morphologies. However, to effectively utilize these nanostructures, their phase, and the formation mechanism with various synthesis parameters need to be fully understood for maximizing their potential. In this study, nanostructured TiO2 are fabricated by using microwave method with various experimental parameters such as in different NaOH concentrations of 4, 6, 8, and 10 M at different hydrothermal treatment temperatures of 100, 120, 140, 150 degrees C, and for the different reaction time of 1, 2, 3, 4 h. The phase and composition of different nanostructures were studied by using X-ray diffraction patterns (XRD) and X-ray photoelectron spectroscopy (XPS). Morphologies of nanostructures were observed by Transmission electron microscopy (TEM). The optical property of the nanostructures was confirmed through the absorption behavior using UVvis spectrophotometer. Diffuse reflectance spectroscopy (DRS) was used to calculate the band gap energies. To confirm the basic properties of the TiO2 nanostructures, the specific surface area was compared. The TiO2 nanostructures fabricated by microwave hydrothermal process have been classified according to the different NaOH concentrations, reaction temperatures, and time. The photocatalytic dye decomposition test for different TiO2 nanostructures was performed under the simulated solar light irradiation. (C) 2015 Elsevier B.V. All rights reserved.