The influence of fluoride ions in oxalic acid electrolyte on the formation of titanium oxide nanotubes was investigated. When titanium is anodized in the absence of fluoride ions, porous titanium oxide arises for oxalic acid concentrations above 0.3 M or for applied voltages above 160 V. However, if 0.1 M fluoride ion is added to oxalic acid, nanotubes are observed at 20 V. By varying the concentration of NH4F to 0.15 M, flowerlike bursts, small pits, or nanorod structures are obtained. X-ray photoelectron spectra were used to show that chemical dissolution increases as the concentration of fluoride ions increases. (C) 2008 The Electrochemical Society. [DOI: 10.1149/1.3054324] All rights reserved.