Due to close boiling points of propane and propylene as well as their low boiling points, distillation separation of propane/propylene mixtures produced at the ethylene center has a large energy demands. Membrane gas separation would be a promising candidate to save separation energy dramatically. In this presentation, we would like to show our recent results on FAU-type zeolite membrane for such C3 mixture separation. FAU-type membrane was synthesized on the outer surface of porous alpha-alumina tube with 10 mm i.d. and 3 cm length (Noritake Co. Limited) by a secondary growth method consisting of seeding of FAU-seeds on the outer surface of support and its hydrothermal growth. The resultant membrane was treated in aqueous solutions containing with a variety of kinds of cation such as alkali and alkaline earth cation, and transition metal cation. Among them, we found that Ag-FAU membrane exceptionally showed high separation factor. For the equimolar C3 gas mixtures, the permeance of propane was 4.13x10-8 mol m-2 s-1 Pa-1 with the separation factor of 55.3 at 353 K.Figure 1 compares the permeances of propane and propylene in the unary and binary systems. Whereas the propylene permeances in the both systems were almost the same, the permeance of propane was markedly decreased in the presence of propylene, indicating that propylene strongly adsorbed in the membrane inhibited the permeation of propane. In addition, such a separation factor exceeding 50 will be able to enable us to produce polymer-grade propylene in one step of membrane separation.