By blending a rigid polymer, sodium alginate ( SA ) , and a flexible polymer, poly ( vinyl alcohol ) ( PVA ) , SA / PVA blend membranes were prepared for the pervaporation separation of ethanol -water mixtures. The rigid SA membrane showed a serious decline in flux and a increase in separation factor due to the relaxation of polymeric chains, whereas the flexible PVA membrane kept consistent membrane performance during pervaporation. Compared with the nascent SA membrane, all of the blend membranes prepared could have an enhanced membrane mobility by which the relaxation during pervaporation operation could be reduced. From the pervaporation separation of the ethanol -water mixtures along with the temperature range of 50 -80ЊC, the effects of operating temperature and PVA content in membrane were investigated on membrane performance, as well as the extent of the relaxation. The morphology of the blend membrane was observed with PVA content by a scanning electron microscopy. The relaxational phenomena during pervaporation were also elucidated through an analysis on experimental data of membrane performance measured by repeating the operation in the given temperature range. SA / PVA blend membrane with 10 wt % of PVA content was crosslinked with glutaraldehyde to enhance membrane stability in water, and the result of pervaporation separation of an ethanol -water mixture through the membrane was discussed. ᭧ 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67: 949 -959, 1998