Pervaporation is a membrane separation process used to separate liquid mixtures Separation is achieved by establishing a concentration vapour-pressure gradient across the membrane. Polyurethane (PU) and polydimethylsiloxane (PDMS) membranes were prepared from their prepolymers by solution casting Dilute aqueous solutions of ethyl acetate, methyl isobutyl ketone, methyl ethyl ketone and aniline were separated using these polyurethane and polydimethylsiloxane polymeric membranes at temperature ranging from 50 to 80°C The effects of the systems operating temperature was studied. The separations were characterised and examined by the effect of temperature on the composition of the retentate and permeate samples taken during the separation process. Gas chromatography was used to analyse the resulting retentate and permeate samples. Extensive physical characterisation of the membranes was carried out using a number of techniques including Scanning Electron Microscopy, gravimetric sorption experiments, Differential Scanning Calorimetry. A combination of the physical examinations and the pervaporation data was used to evaluate the membranes performances in the separation of all four solutions within the temperature range examined. Higher selectivity values were obtained for separations carried out using the polydimethylsiloxane membrane whereas higher flux values were achieved using the polyurethane membranes. The most successful separations, based on selectivity and flux values, was deemed to be the separation of methyl isobutyl ketone and water at 80°C using the polydimethylsiloxane membrane, PDMS1, with selectivity and flux values reaching 774 and 0 400kg/m2hr, respectively. Some of the physical charateristics of the membranes which were examined, such as the activation energy of permeation and the glass transition temperature, were found to be unsuitable for use as prediction methods for the performance of a particular membrane/liquid mixture system. The most preferable membrane preparation conditions were also isolated during the course of this study with the aid of scanning electron microscopy images.