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Nanostructured amorphous and anatase TiO(2) are both considered as high rate Li-insertion/extraction electrode materials. To clarify which phase is more desirable for lithium ion batteries with both high power and high density, we compare the electrochemical properties of anatase and amorphous TiO(2) by using anodic TiO(2) nanotube arrays (ATNTAs) as electrodes. With the same morphological features, the rate capacity of nanostructured amorphous TiO(2) is higher than that of nanostructured anatase TiO(2) due to the higher Li-diffusion coefficient of amorphous TiO(2) as proved by the electrochemical impedance spectra of an amorphous and an anatase ATNTA electrode. The electrochemical impedance spectra also prove that the electronic conductivity of amorphous TiO(2) is lower than that of anatase TiO(2). These results are helpful in the structural and componential design of all TiO(2) mesoporous structures as anode material in lithium ion batteries. Moreover, all the advantages of the amorphous ATNTA electrode including high rate capacity, desirable cycling performance and the simplicity of its fabrication process indicate that amorphous ATNTA is potentially useful as the anode for lithium ion batteries with both high power and high energy density.