The self-diffusion of water, ethanol and water-ethanol mixtures in polyacrylic acid (PAA) and PAA-polysulfone (PSF) composite membranes was measured with pulsed-field gradient (PFG)-nuclear magnetic resonance (NMR) spectroscopy. The partial solubilities and self-diffusion coefficients were obtained. An attempt was made to explain the transport properties of water and ethanol through the PAA layer and PAA-PSF composite membranes. It was concluded that there are two types of channels for diffusate transfer in PAA : an ionogenic hydrophilic channel which is selective for water and a hydrophobic channel which contains a predominance of ethanol molecules. The existence of aluminum nitrate in PAA influences the morphology of the latter channel, There is a good agreement between of the separation factors estimated from PFG-NMR data and those obtained by pervaporation testing.