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A facile method to produce very hydrophobic surface was developed simply using the mixture of TiO2 nanoparticles and poly(methyl methacrylate) (PMMA). When the volume ratio of TiO2 to PMMA is between 35 vol.% and 50 vol.%, the mixture of two hydrophilic materials became very hydrophobic. Analysis of the molecular structure by infrared spectroscopy shows that the preferential orientation and attachment of a carbonyl group of a polymer molecule to the surface of TiO2 nanoparticles play a critical role in the appearance of the strong hydrophobicity. When this composite was exposed to UV light, PMMA on the surface of the mixture film was decomposed through a photocatalytic reaction and the very hydrophobic surface turned to the superhydrophilic one. The superhydrophilic property of UV-irradiated composite lasts as long as several months. This long lasting superhydrophilicity is ascribed to the porous structure, which provides high roughness and strong capillary interaction. Easy transition from strong hydrophobicity to superhydrophilicity in TiO2/PMMA composites could be applied to designing high contrast hydrophilic/hydrophobic patterns. (C) 2011 Elsevier Inc. All rights reserved.