A series of sodium alginate-gelatin polyelectrolyte complex (PEC) membranes were prepared by physical blending and utilized for propylene dehydration. The chemical and physical structures of the membranes were characterized by scanning electron microscope (SEM), Fourier transform infrared (FT-IR), X-ray diffraction (XRD), differential scanning calorimetry (DSC), and positron annihilation lifetime spectroscopy (PALS). To elucidate the structure-performance relationship, water vapor sorption and diffusion properties were investigated. For dehumidification tests, the water vapor permeance and water/propylene selectivity increased simultaneously with the gelatin content because of enhanced water uptake and reduced free volume cavity size. When gelatin content was 60 wt.%, the PEC membrane exhibited the highest permeance of 39.8 m(3)(STP)/(m(2) h bar) and an infinite permselectivity, which far outperformed the pure sodium alginate membrane and gelatin membrane. A tentative explanation for this interesting result was presented taking into account of the competition of sorption and diffusion. (C) 2011 Elsevier B.V. All rights reserved.