room temperature NH3gas sensors based on Pt and Pt-Ir (Ir doping Pt) porous ceramic electrodes havebeen fabricated by both electroplating and sputtering methods. The properties of the gaseous ammo-nia sensors have been examined by polarization and chronoamperometry techniques. The influence ofhumidity on the features of the resulting sensors in the system has also been discussed, and the work-ing potential was optimized. Water vapors seem to hugely improve the electrochemical activity of theelectrode. With increasing the relative humidity, the response of the Pt-Ir(E)/Pt(S)/PCP sensor to NH3gascould be enhanced remarkably, and the sensitivity increases from 1.14 to 12.06 A ppm−1cm−2.Thenwe have also discussed the sensing mechanism of the Pt-Ir sensor and the result has been confirmed byX-ray photoelectron spectroscopy of the electrode surface before and after reaction in the end.