Composite membranes with ultrathin separation layer were prepared by alternating electrostatic adsorption of cationic and anionic compounds (polyelectrolytes and bolaamphiphiles) at porous supporting membranes such as Celgard 2400, PAN/PET (a polyethyleneterephthalate fleece coated with a thin layer of polyacrylonitrile) and Isopore (an etched ion-track polycarbonate membrane). As the ionic compounds poly(allylamine hydrochloride) (PAH), poly(styrenesulfonate sodium salt) (PSS), 1.4-diketo-3,6-diphenylpyrrolo-[3,4-c]-pyrole-4,4'-disulfonic acid and 10,12-docosadiyne-1,22-disulfate disodium salt were used. The composite membranes were studied on their gas permeation and pervaporation properties. The adsorption of 20 layer pairs of PAH/PSS at PAN/PET membranes was sufficient to reduce the argon flow to 7% of the initial value, while 60 bilayers reduced the flow to 0.1%. Gas flow rates of oxygen, nitrogen and argon were nearly identical, while the flow rate of carbon dioxide was higher by a factor of up to 2.4. Toluene/heptane pervaporation through composite membranes of 60 bilayers of PAH/PSS on PAN/PET gave a toluene enrichment from 20% in the feed to 24% in the permeate, while for ethanol/water permeation a water enrichment from 3% in the feed up to 50% in the permeate was found.