We report a method for synthesizing TiO2 nanostructures by applying microwave irradiation (1200 W, 2.45 GHz, single-mode) to a Ti substrate under an atmosphere comprising of O-2 and Ar. After 1200 W microwave irradiation, one-dimensional (1D) nanostructure arrays were synthesized on the surface of the substrate. The average dimensions of the 1D structures were 200 nm in length and 30 nm in diameter. The structures were single crystalline. The EDX elemental maps of the areas examined using HAADF-STEM demonstrated that Ti and O were distributed homogeneously throughout the nanostructure. Quantitative analysis of the mean atomic ratios in the nanostructures disclosed a Ti:O ratio of 0.331:0.669. XPS analysis demonstrated that the predominant oxidation state of Ti in the samples was +4. On the basis of these results, we propose a possible mechanism for the formation of the TiO2 nanostructures via microwave irradiation. (C) 2010 Elsevier B.V. All rights reserved.