We have found that a copper ion-exchanged MFI (Mobil Five)-type zeolite, having an ion exchange capacity of 112% (CuMFI-112), exhibits a specific interaction with CH4, even at room temperature. The observed properties are very remarkable compared with those found in the adsorbed amount of sodium ion-exchanged MFI and in the interaction with the sodium ion in MFI as well as in the adsorbed amounts for other types of copper ion-exchanged zeolites. The specificity of Cu+ in MFI is clearly evident. The most remarkable feature of the present system is the distinct appearance of infrared bands (IR) at 2661 and 2619 cm−1 due to adsorbed CH4 at 300 K and the change in the X-ray absorption fine structure spectra of CuMFI before and after CH4 adsorption at 300 K, indicating the existence of substantial and specific interaction in this system. In addition, calculations based on the density functional theory were carried out by utilizing a Cu−AlSi91O151H66 cluster model, which is made up of a 10-membered ring of CuMF...