Incorporation effects of fluorinated alkyl side groups into polyimide membranes on their pervaporation properties were investigated for several dilute aqueous organic solutions. The pervaporation experiments were carried out as functions of the nature of permeating solvents, feed concentration, permeate pressure and feed temperature. The polyimide membranes containing fluorinated side groups showed high pervaporation selectivity and high permeating flux towards hydrophobic solvents. They were explained in terms of their enhanced sorption/sorption selectivity and concentration-average diffusion coefficient/diffusivity selectivity towards organic solvent over water due to enhanced hydrophobicity and increased fractional free volume (FFV) obtained by the introduction of fluorinated side groups.