In this paper, we present results of comparative studies on the photocatalytic activity of microporous and nanoporous titanium dioxide (TiO2) layers formed on titanium substrates by electrochemical anodization at different voltages. Two sample groups each including four samples was prepared for microporous and nanoporous TiO2 layer formation. Microporous TiO2 layers were prepared in 1 M H2SO4 solution in 10 min. Nanoporous TiO2 layers were formed in %1 HF solution in 30 min and then annealed at 480 degrees C in ambient air. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and atomic force microscopy (AFM). The photocatalytic activity of the samples was determined by assessing the decomposition rate of methylene blue (MB) solutions under UV light for different periods of time. By using the data obtained from the UV-Visible spectrophotometer, photocatalytic decomposition kinetics was also determined. The results indicated that nanoporous TiO2 layers formed by applying 20 V showed optimal photocatalytic performance, whereas the sample anodized at 250 V exhibited the highest photocatalytic activity within its own sample group, nearly matching the photocatalytic activity of the highest performing sample. (C) 2015 Elsevier B.V. All rights reserved.