Thin films (thickness : 0.2 to 2 mum) of Li-Al-O mixed oxides were obtained by rf-magnetron sputtering in order to prepare ionic conductors. The stability, microtexture and composition of the deposits depend closely on the operating conditions. The conductivities of these films were measured using the complex impedance method. Their electrical conductivity follows an Arrhenius law and exhibits a maximum for a lithium content corresponding to a Li/Al ratio of 0.13.