The simulations and the experimental data of ionic transport across a bipolar membrane in dialysis systems of a 2-1 type salt, where "2-1 type" means a combination of a bivalent cation and a univalent anion, show that the transport properties of a 2-1 type salt in the system have features different from those of a 1-1 type. (univalent cation and univalent anion) salt in the following points : (1) the potential of a 2-1 type salt system has a constant value irrespective of the charge density ratio of the two charged layers when the membrane charge densities are much larger than the concentration of the salt solutions; (2) the potential-concentration curves have a peak under suitable conditions; (3) the permeability coefficient of the salt has a different value between two dialysis systems where the direction of the positive-negative layered structure of the membrane is reversed even if the mobility of the cation is the same as that of the anion.