A calix-conjugated thermo-responsive hydrogel containing 15% tetra(5-hexenyloxy)-p-tert-butylcalix[4]arene (HBCalix), P(NIPAM-co-HBCalix), was used to remove nickel(II) ions from water. Both thermo-sensitive properties and the Ni2+-adsorption capabilities of the prepared P(NIPAM-co-HBCalix) hydrogels are investigated. Introduction of the monomer HBCalix considerably enhanced the adsorption of Ni2+ onto the hydrogel by chelation between hexenyloxy groups and metal ion. When HBCalix units capture Ni2+ and forms HBCalix/Ni2+ hostguest complexes, the lower critical solution temperature of the hydrogel shifts to a higher temperature due to both the repulsion between charged HBCali/Ni2+ groups and the osmotic pressure within the hydrogel. Adsorption studies were carried out by varying contact time, counter ion and initial concentration of Ni2+. The evaluation of adsorption properties showed that the hydrogel exhibited better correlation with Langmuir isotherm model. P(NIPAM-co-HBCalix) could be used repeatedly with little loss in adsorption capacity by simply changing the environmental temperature. This kind of ion-recognition hydrogel is promising as a novel adsorption material for adsorption and separation of Ni2+ ions. (c) 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 2401-2408