The electrolytic conductivities of aqueous solutions of potassium and sodium phosphates were measured over the temperature range 25-325 degrees C for phosphate concentrations of 0.0005-0.0100 M. The salts investigated were, potassium dihydrogen phosphate, potassium monohydrogen phosphate, and potassium phosphate, and the corresponding sodium salts. At all temperatures and concentrations investigated, the conductivities of the potassium salts were higher than those of the sodium salts.