Synthesis conditions of La2Mo2O9 thin film by radio frequency (RF) sputtering technique on Al2O3 ceramic substrates are studied. It is found that the deposition temperature and oxygen partial pressure are the most important factors for obtaining pure La2Mo2O9 films. Varying both parameters, Mo-rich, stoichiometric, and Mo-deficient films are obtained. With increasing the La:Mo ratio, films become denser. A crust layer is observed on top of the Mo-rich and the Mo-deficient films. The formation of the La2Mo2O9 phase is discussed with respect to the sputtering mechanism. (c) 2005 Elsevier B.V. All rights reserved.