Spontaneous sequential adsorption of poly(allylamine hydrochloride) and poly(sodium styrene sulfonate) (layer-by-layer deposition) onto surface-oxidized poly(4-methyl-1-pentene) film was studied with the objective of creating an asymmetric gas separation membrane consisting of a thin multilayer barrier layer on a more permeable polymer film. Poly(4-methyl-1-pentene) film was first surface-oxidized with chromic acid solution to introduce carboxylic acid functionality to the surface for depositing the first layer. By alternating the poly(allylamine hydrochloride) and poly(sodium styrene sulfonate) depositions, multilayered structures were prepared with the total number of layers up to 104. Gas permeabilities of composite membranes prepared by this layer-by-layer deposition technique were determined for hydrogen, oxygen, and nitrogen. The depressed gas permeabilities of the composite membranes are explained by dense and rigid packing of the polyelectrolytes in stratified layers. The multilayered poly(allylamine hydrochloride) and poly(sodium styrene sulfonate) structures were shown to be 18 000 times better barriers to nitrogen than poly(4-methyl-1-pentene). Alternating deposition of polyaniline and poly(sodium styrene sulfonate) into stratified multilayers on surface-oxidized poly(4-methyl-1-pentene), on the other hand, did not change the permeability properties of the film, suggesting a loose packing of molecules in the layers.