Nanosized sodalite octahydrate zeolite has been developed using a crystallization room temperature in the absence of organic templates. The best aging time found was 120h and in this time the nanosized sodalite octahydrate zeolite is formed. The samples were characterized by x-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier-Transform Infrared (FTIR) spectroscopy, x-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), and N-2 adsorption-desorption isotherm. The equilibrium adsorption capacities of pure gases CO2 and CH4 were measured at 298 and 308K up to 20bar on both powder and granules of sodalite octahydrate zeolite. With increasing temperature, the adsorption capacity decreases for both sodalite octahydrate zeolite powder and granules. The selectivity of CO2 at 308K over CH4 was 6.53.