This paper reports the results obtained by studying the ion-exchange synthesis of potassium hydroxide from lime milk and carboxylic resin Lewatit CNP 80 in the K-form. Carboxylic resin has been shown to have several advantages in comparison with, for example, sulfonate ion exchanger, due to its higher selectivity toward Ca2+, which substantially enhances at elevated temperature. The increase of temperature from 293 to 333 K enhances the sorption of Ca2+ versus K+ that allows achieving far higher KOH concentration in the solution phase. The values of equilibrium separation factor, or, for Ca2+-K+ exchange have been determined at 293 and 333 K by varying the equivalent fraction of Ca2+ in the solution phase from 0.04 to 0.7. A remarkable increase of ct values has been observed at higher temperatures and at low calcium content in the solution phase. The regeneration of the resin (conversion from Ca- to K-form) has been carried by using the mixtures of potassium chloride and potassium sulfate. The regeneration process under these conditions is accompanied by the ion-exchange isothermal supersaturation of calcium sulfate, which forms a stable supersaturated solution in the resin bed. After leaving the column, CaSO4 crystallizes spontaneously, which allows reuse of the regenerating solution following the complete elimination of the Ca2+ admixture with a small amount of K2CO3. The precipitates of calcium sulfate and calcium carbonate are the only wastes produced in the process. The complete regeneration of the resin has been shown to require a nearly 70-fold excess of the regenerant; nevertheless, the decrease in the degree of resin regeneration from 100 to 80% allows reduction of the amount of the regenerant by more than 2 times. The use of incompletely regenerated resin for the synthesis of KOH does not decrease remarkably the efficiency of the process. The flow sheet of the proposed process is presented and discussed.