The extraction of caesium by resorcinol based resins was investigated. At high hydroxide concentration ([OH-] = 0.15 M), the alkali-metal cations' sorption selectivity (determined in competitive extraction system) for resorcinol resins was found to be Cs+ > Li+ > Rb+ > K+ > Na+, whereas at pH 7 this selectivity was found to be Cs+ > Rb+ > K+ >> Na+ approximate to Li+. Different mechanisms of ion exchange occurring in these phenolic resins can explain this selectivity series. Then different macrocycles were incorporated in the resins. The ionoselective properties of these new ion-exchange resins are strongly influenced by the nature of the crosslinker. The presence of macrocycles lead to an improvement of selectivity towards caesium in relation with the size of the macrocycles introduced.