An integral ion selective electrode for the analysis of a potassium ion comprising a support, an electroconductive metal layer such as a silver metal layer, a layer of a water-insoluble salt of said metal such as a silver chloride layer, an electrolyte layer which comprises an electrolyte salt of a potassium ion with the same anion as the anion of the water-insoluble salt, said electrolyte layer being substantially free from a binder, and an ion selective layer, which is characterized in that the electrolyte layer comprises crystalline electrolyte having a mean crystal size of not more than 60 .mu.m. Processes preferably employable for the preparation of the ion selective electrode are also disclosed.