an ion - selective electrode for measuring carbonate concentration comprising a conductive metal layer , a halide of said conductive metal layer , a carbonate ion - selective layer containing ion carrier , and a buffer layer containing a hydrophilic polymer binder and a buffer laminated in this order on an electrically insulating support , and a pair of the above electrodes . it is characterized by not having the electrolyte layer containing hydrophilic polymer binder , having the possibility of degradation of the electrolyte layer by the absorption of moisture being extremely little , and having a good stability in the course of time . in the electrode of the invention , the ion - selective layer comprised of hydrophobic organic material is directly laminated on the metal halide layer , the adhesive strength between the metal halide layer and the ion - selective layer is sufficient , the strength of the ion - selective layer is sufficiently great , and which is stable . the electrode of the invention has a sufficient buffering ability , and it requires neither operation of preliminary measurement of the ph value of aqueous liquid sample nor fixation of the ph value by adding a ph buffer to sample . moreover , the adverse affect by the interfering substance such as salicylate , p - aminosilicylate or gentisate is eliminated or remarkably reduced .