For the separation of methanol/MTBE (methyl tert-butyl ether) mixtures, methanol selective chitosan composite membranes were prepared and tested for pervaporation experiments. When anionic surfactants are added into the cationic chitosan solution, the solution viscosity was drastically decreased due to the collapsed chain conformation. Pervaporation characteristics of surfactant modified chitosan membrane were substantially improved due to the decreased membrane thickness and possible enhanced affinity to methanol. Rheological data of the casting solution was measured using viscometer and the surface morphology of the surfactant complexed chitosan membrane was investigated by atomic force microscopy (AFM).