Ion-exchange resins are prepared by introducing phosphonic acid monoethyl ester or phosphonic acid groups into formaldehyde condensation poly(dibenzo-18-crown-6) resin. The phosphonic acid ion-exchange groups provide accessibility for metal cations, while the ion-selective cyclic polyether binding site influences the selectivity. The selectivities and efficiencies for competitive alkali-metal cation sorption from aqueous solutions by these crown ether-containing phosphonic acid resins are strongly influenced by the pH of the aqueous solution, the identity of the phosphonic acid groups, and the molar ratio of ion-exchange groups to crown ether units.