Novel cellulose membranes were prepared by using amine oxides as its solvent. Steady-state gas permeation rates in a “water-swollen”α-cellulose membrane were measured at various temperatures.The function of water on α-cellulose membrane was also revealed by comparatively studying the gas permeability of cellulose acetate membrane

benzoylated cellulose membrane and polysulfone membrane in “dry” and “wet” state. The effect of swelling on permeability of α-membrane was studied in some details. The difference of gas permeability between “dry” and “water-swollen”α-cellulose membrane was investigated. The permeability of CO2 was as high as 130 barrer［1 barrer=7.5×10-14cm3(SPT)·cm·(cm2·s·Pa)-1］; the separation factor of CO2/H2 can be up to 15.