A series of lead-sensitive poly(N-isopropylacrylamide) microgels with pendant crown ether groups were prepared. Their cation-sensitive behaviors were studied by dynamic light scattering When ionic strength is not controlled, adding salts causes the microgel particles to deswell However, when the salt effect is ruled out by keeping a constant ionic strength, adding Pb-2I results in much larger swelling The Pb-21-induced swelling was explained by the formation of hostguest complex between Pb2- and the pendant crown ether groups, which increases the hydrophilicity of the polymer and accordingly the degree of swelling The lead sensitivity of the microgels increases with increasing crown ether content For the modified microgel with the highest crown ether content, it swells to similar to 430% of its original volume at [Pb2+] = 10 mM Other cations also increase the swelling degree of the modified microgels The extent of the cation-induced swelling mainly depends on their affinity to the pendant crown ether groups 0 (C) 2010 Wiley Periodicals, Inc J Polym Sci Part A Polym Chem 48 4120-4127, 2010