An object of the present invention is to provide a planar ammonia selective sens-ing electrode and a manufacturing method thereof. The planar ammonium ion sensing layer and the planar hydroxide ion sensing layer are disposed on an elec-tric-conductive by a drop-coating method, a sputtering method, an electrodeposi-tion method or a screen-printing thick-film technique, so as to improve the accu-racy and reduce the volume of the sensing electrode. At the same time, the planar ammonia selective sensing electrode is provided with the high selectivity and the high sensitivity to be applied in the fields of the medicine, the biochemistry, the chemistry, the agriculture, the environmental and others. For example, it can be applied to monitor the variation of the ammonia and nitrogen concentrations dur-ing the planting process of hydroponic plants, the variation of the ammonia and nitrogen concentrations of the human sweat, the water quality of the aquaculture, or the specific biological indicators (e.g. creatinine) by means of combining the specific enzymes.