This paper is concerned with the study of metallorganic chemical vapor deposition (MOCVD) anatase film growth, with the aim of assessing the relationship between the TiO2 surface morphology and the photocatalytic properties of the films, particularly their relation to the decomposition of ethylbenzene at 50 mu g m(-3) in humidified air. We have found an interesting relationship between the structural properties of TiO2 films deposited by MOCVD at 400 degrees C for different deposition times. We observed the maximum efficiency of films in the thickness range of 600-900 nm, while in a higher thickness, this activity relentlessly decreased. From atomic force microscopy analysis, it was ascertained that this reduction was not due to a decrease in the superficial area, which showed a constant roughness of films thicker than 600 nm. From X-ray diffraction analysis, the films always grew in the anatase TiO2 structure, but the thicker the films, the more pronounced the (100) preferred orientation. Thanks also to theoretical considerations, it was concluded that the activity decrease in the 900-1800 nm thickness range was due to the particularly strong increase in the (100) plane-oriented crystallites recorded in the same range, causing a decrease in surface energy and, contemporaneously, a hindering effect on photocatalytic activity. (C) 2009 The Electrochemical Society. [DOI: 10.1149/1.3236502] All rights reserved.