The invention relates to a process for preparing multilayer nanoporous films of SnO/CoOwhich may be used as sensitive films for surface acoustic wave sensors, SAW, for ammonia detection. According to the invention, the process consists in successively irradiating some Co and SnOtargets (7 and 6), respectively, placed inside an irradiation enclosure (4), with a beam (11) coming from a pulsed laser (12), the material (8) resulted after the laser ablation of the targets (7 and 6) being deposited directly on the surface of a SAW sensor (5) as a multilayer sensitive film, both component layers being nanoporous.