Abstract: A device useful for separating the components of gas mixtures includes a selectively gas permeable mixed matrix membrane of a dispersed phase of chabazite type molecular sieve particles uniformly distributed throughout a continuous phase of a polymer. The membrane can be fabricated by dispersing the chabazite type molecular sieve particles in a solution of the polymer dissolved in a suitable solvent, and then forming the suspension into a membrane structure by conventional polymer membrane fabrication techniques. Mixed matrix membranes with chabazite type molecular sieves are well suited to separations of oxygen, carbon dioxide or helium from nitrogen or methane.