Ion exchange can be an appropriate method for the removal of a valuable ion like caesium from polyether polyols. CsOH has recently demonstrated to have improved properties as catalyst for these polymerization reactions. After completion of the polymerization reaction, the initiator has to be removed from the polyol. Such a process requires not only the complete elimination of the catalyst, also its complete recovery in order to make the process economically feasible. In order to develop an optimized ion exchange process, equilibrium, kinetics, regeneration and final purification of caesium have been studied. A quasi-irreversible equilibrium isotherm was obtained for the system Amberlite 252-Cs in polyol media. The useful capacity of the resin for Cs in polyol media is 3.8 meq/g. The influence on the exchange rate of the stirring rate, resin to bulk ratio, initial caesium concentration and the type of cation removed have been analyzed. It has been seen that a minimum resin/polyol ratio of 56 g/kg of polyol is necessary to obtain a suitable exchange rate. Caesium final level in polyol (<5 mg/kg) is well under the commercial specifications required for this kind of products. Although the removal of caesium ions is slower than the potassium ions and this one slower than sodium, the differences between them are not excessively shown, as expected, that the size of the ion is not so important as the molecular weight of the polyol. The caesium hydroxide after the regeneration process of the resin can be effectively recycled to the process by means of an anion exchange resin. (C) 2005 Elsevier B.V. All rights reserved.