Polycrystalline spinel Zn2SnO4films were successfully deposited on alumina substrates by spray pyrolysis. It was found that the ratio of the two cations in the films obtained differs considerably from the ratio in the initial solutions. By optimizing the solution compositions and the deposition and heat-treatment parameters, it was possible to obtain homogeneous single phase films with good adhesion to the substrate. At room temperaturethe electrical resistance of the films was strongly dependent on humidity, the response and recovery times being very short (1-2 min). The humidity sensing characteristics deteriorated in the presence of a binary oxide (ZnO or SnO2) impurity in the film. © 1997 Academic Press.