Asymmetric polyetherimide membranes were prepared using the dry/wet phase inversion technique and tested for the pervaporation of aqueous isopropanol solutions. The effects of four major variables involved in the membrane preparation procedure, including polymer concentration, additive content, solvent evaporation temperature and period, on membrane performance were investigated. Factorial design experiments were carried out to identify the factor effects. It was shown that the aforementioned independent variables interacted with respect to the pervaporation performance of the resultant membranes. An individual interaction effect was in general less significant than the main effects; however, the combined influence of the various interaction effects could not be neglected. The overall effect of an individual variable at the selected conditions of other variables on the membrane performance was also illustrated explicitly.