The possibility of fabricating a highly regular nanohole array using different acid mixtures for the anodic oxidation of aluminum was investigated. The regularity of a nanohole array formed using a 1: 1 sulfuric/oxalic acid mixture was quantified. Excellent regularity was obtained at around an anode voltage of 32 to 36 V. Cell pitch of the nanohole array at 36 V was 73 nm, which falls between those obtained using sulfuric acid (65 nm at 28 V) and oxalic acid (95 nm at 40 V). The present results strongly suggest that the pitch of the regular nanohole array can be varied by changing the ratio of the different acids. (C) 2004 The Electrochemical Society.