The swelling behavior of perfluorinated ionomer membranes in various solvents were studied. It was found that the sample pretreatments and the type of the functional group have a strong effect on the swelling properties of these membranes. The swelling of sulfonate membrane is higher than that of the carboxylate membrane. Also, the membrane swelling can be increased by quenching the sample and increasing solvent temperature. Finally, the dissolution properties of this membrane are discussed.