The effect of temperature on the exchange of di- and monovalent ions on polymethacrylic and polyacrylic cation exchangers in the range from 298 to 413 K is studied. It is shown that the differential enthalpy and the equilibrium coefficient simultaneously increase with temperature. The dependences of the enthalpy on temperature are linear. The effect of temperature on the enthalpy of ion exchange observed for all studied ion exchangers is much more strong than in the systems described in the literature with sulfonic acid cation exchangers and highly basic anion exchangers. The problem of taking into account the dependence of enthalpy on temperature when predicting the behavior of ion-exchange systems is discussed.