Highly ordered TiO2 nanotube array prepared by electrochemical anodization generates considerable interest as a practical air purifier, since a nanotube array can form a TiO2 film with a porous surface and straight gas diffusion channel, simultaneously reserving enough geometric thickness. Here, we reported on the application of highly ordered TiO2 nanotube arrays with different lengths for degradation of gaseous acetaldehyde pollutants in air. The results showed that increasing the lengths of nanotube arrays within a certain range could significantly improve the degradation rate of acetaldehyde molecules. The main product of acetaldehyde degradation was detected to be CO2, which indicated that the mineralization of acetaldehyde molecules was the major process in this photocatalytic reaction. When compared with a P25 TiO2 nanoparticulate film with similar thickness and geometric area, in the initial degradation of acetaldehyde, the nanotube array did not show obvious superiority. However, in the subsequent degradation, the nanotube array demonstrated an enhanced photocatalytic activity. It was suggested that this enhancement resulted from the special infrastructure of the nanotube array, which was favorable for the diffusion of intermediates and the reduced deactivation of photocatalyst in the photocatalytic reaction.