Pervaporation separation of water-ethanol was carried out with polyion complex membranes based on k-carrageenan. The polyion complex membranes were prepared by the ion complex formation between k-carrageenan (anionic polymer) and poly{1,3-bis[4-alkylpyridinium]propane bromide}s (cationic polymers) with different numbers of methylene units between two ionic sites within a repeating unit, respectively. The ion complex membranes were characterized with FT-IR, X-ray diffractometry. Dehydration of 90 wt % aqueous ethanol solution was carried out at different temperatures (30, 40, 50, and 60 degrees C). The selectivity and permeability through them were very good over a wide temperature range; in the case of the polyion complex membrane consisting of k-carrageenan and poly{1,3-bis[4-ethylpyridinium]propane bromide}, the permselectivity was 45,000 and permeability was 150 g/m(2) h at 30 degrees C. With increasing operating temperature, the permeability was increased highly but the selectivity decreased slightly.