The trivacant Keggin-type polyoxometalate Na(10)-alpha-SiW(9)O(34) (SiW(9)) was encapsulated by the cationic surfactant dimethyl dioctadecylammonium (DODA) and forms an organic-inorganic complex. Stable Langmuir monolayers of this surfactant-encapsulated cluster complex form at the air-water interface and can be transferred onto solid substrates with a transfer ratio of 1.0 +/- 0.02. Fourier transform infrared spectroscopy at grazing incidence reflection condition reveals that the non-centrosymmetric SiW(9) clusters are highly oriented in the films with their symmetry axis aligned preferably perpendicular to the layer plane. We propose a model in which the orientation state of SiW(9) is induced by the different electrostatic interactions between DODA molecules and different positions at the SiW(9) surface. (C) 2010 Elsevier B.V. All rights reserved.