In this work, the possibility to detect ppm ammonia concentrations in water environment, at room temperature, by means of Standard Optical Fibers (SOFs) sensors coated by Metal Oxides (MOXs) films has been demonstrated. Electro-spray pyrolisis technique has been used to deposit SnO2 films onto the distal end of single-mode optical fibers. This deposition technique allows the possibility to tailor the fabricated films properties by varying the deposition parameters, such as the metal chloride concentrations, the solution volume and the substrate temperature. The sensor operating principle relies on the measurement of the light intensity reflected by the fiber-sensitive layer interface: the pollutant molecules adsorption within the MOX film causes a change in its complex dielectric function and thus in the fiber-film reflectance. Spectral characterization of the obtained sensing probes has been carried out in the range 400-1750nm. Single wavelength reflectance measurements have been carried out to test the sensor performances for ppm ammonia detection. High sensitivity to the target analyte, response times of approximately 10-20 minutes and a Limit Of Detection as low as sub-ppm has been observed.© (2005) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.