The effect of Na-alginate content on the gas permeation properties of water-swollen membranes prepared by varying Na-alginate and poly(vinyl alcohol) (PVA) content in membranes was investigated. The influences of water content and crystallinity of the membranes on the gas permeation performance of the water-swollen membranes were studied. The gas permeation rate and selectivity of Na-alginate/PVA water-swollen membranes were compared with those of the dry membranes. The permeation rates of nitrogen and carbon dioxide through water-swollen membranes were in the ran e of 0.4-7.6 X 10(-7) to 3.7-8.5 X 10(-6) cm(3) (STP)/cm(2) s(-1) cmHg(-1), which were 10,000 times higher than those of dry-state membranes. The permeation rates of mixture gases through water-swollen Na-alginate/PVA membranes were found to increase exponentially with the increase of Na-alginate content, whereas carbon dioxide concentration in permeates was decreased linearly. It was found that the gas permeance of the water-swollen membranes increased with increasing the Na-alginate content in the membrane. Gas permeation rates of the water-swollen Na-alginate/PVA membranes increased with increasing the water content in the membrane and decreasing the crystallinity of the membrane. (C) 2004 Wiley Periodicals, Inc.