Abstract: Provided is a water vapor adsorption-desorption material in which a substance having a LCST is uniformly retained inside pores of a mesoporous body, which can reduce energy required for regeneration, and a method for measuring LCST behavior capable of measuring LCST behavior of an ionic liquid used in the water vapor adsorption-desorption material without errors. The water vapor adsorption-desorption material includes a mesoporous body and an ionic liquid retained inside pores of the mesoporous body, the ionic liquid exhibiting LCST behavior, and the method for measuring LCST behavior of an ionic liquid used for a water vapor adsorption-desorption material, the method including detecting a change of hydration/dehydration state of a mixture of the ionic liquid and water as electric signals, by means of AC impedance measurement.