PURPOSE: To selectively adsorb and separate CO2 and water if exists, by bringing a mixture of hydrocarbon and CO2 into contact with an adsorbent including clinoptilolite.

CONSTITUTION: When CO2 contained in a slight amount is separated from a mixture of hydrocarbon of not more than 5 of dynamic diameter and the CO2, the mixture is brought into contact with a clinoptilolite adsorbent. The ion exchange for clinoptilolite is performed until at least 40% of ion exchangeable non-Na cations are substituted by Na cations, to obtain Na clinoptilolite (the primary ion exchange step), the resulted Na clinoptilolite is mixed with a binder to form pellets and the secondary ion exchange step is performed by using a cation such as Li, K, Ca, Zn, Cu, Co, Fe or the like. The desorption of CO2 is performed by passing an inert gas of not less than 50°C through the adsorbent.