The polyion complex composite (PIC) membranes were prepared by the complexation of the ionic groups of sodium alginate and chitosan, and the pervaporation characteristics were investigated for the separation of MTBE/methanol mixtures. The polyion complex reaction took place by the ionic crosslinking reaction between the carboxylate groups (-COO-) of sodium alginate and the protonated amine groups (-NH3+) of chitosan. The polyion complexation depended upon the content of counter ions. In this study, the prepared membranes showed excellent pervaporation performance in the separation of MTBE/methanol mixtures. Especially, PIC membrane prepared from 2.0 wt.% SA solutions and 2.0 wt.% chitosan solution appeared to permeate only methanol from the feed, with the flux of over 240 g/m(2) h. As the operating temperature increased from 40 to 55 degrees C, the permeation rate of methanol increased, but that of MTBE decreased. These results were due to the physicochemical and structural properties of polyion complex membranes.