A reference electrode having a casing with an inner cavity successively filled with a paste constituting an active material and a porous material impregnated with an electrolyte solution. The projecting end of a silver wire is embedded in the paste at the bottom of the inner cavity. The paste is constituted of a powder of a silver compound and of the alkaline electrolyte solution. The silver compound is any insoluble silver salt or oxide containing the negative ion of the electrolyte solution. The impregnated porous material is preferably constituted by a plurality of mat separator pieces mechanically and compressed by a closing plug, closing the inner cavity and forming a porous liquid junction.