We describe a simple method of fabricating a superhydrophobic carbon nanotube (CNT) film without any chemical modification. A remarkable surface wettability transition between superhydrophobicity and superhydrophilicity can be easily observed by the alternation of UV irradiation and dark storage. The adsorption and desorption of surface water molecules on the CNT surfaces account for their tunable surface wettability, which is disclosed by X-ray photoelectron spectroscopy analysis. We also perform a series of comparison experiments to confirm the explanation of its distinctive surface wettability. This switchable wettability on the CNT film could have potential applications in areas requiring multifunctional CNT-based films.