In this article, organic/inorganic membrane was prepared for gas separation by incorporating dodeca-tungstophosphric acid (PWA) into the base polymer. Flat-sheet composite membranes were produced via dry-phase inversion method. In the first stage, the effects of PWA concentration on morphology and performance of polyvinyl alcohol (PVA) membranes were elucidated. For this stage, the preparation of membranes was carried out at constant temperature of 40 degrees C. The porosity of the prepared membrane was slightly increased with addition of PWA. By increasing the PWA concentration up to 6 wt % in the membrane recipe, the permeability of N-2, O-2, and air was improved from 50,000 (for no addition of PWA) to around 160,000, 140,000, and 80,000 L m(-2) h(-1), respectively. For H-2, this was enhanced from 110,000 to 230,000 L m(-2) h(-1). The ideal selectivity of the membrane was slightly improved for N-2/air (from 1 to 1.2). For N-2/O-2 pair, the initial drop (from 2.5 to 1.5) was followed by a slight increase (1.5-1.9). Moreover, the selectivity was decreased for H-2/air (from 2.8 to 1.8) and H-2/N-2 (from 2.2 to 1.7) by increasing the PWA concentration. The 10 wt % PVA membrane with 6 wt % PWA demonstrated superior performance compared with the other compositions. In summary, the presence of PWA in the casting solution results in lower flux for O-2 and higher selectivity for H-2/O-2 pair. In the second stage, the effects of solvent evaporation temperature (10, 27, 40, and 80 degrees C) on morphology and performance of the membranes were studied. By increasing the temperature, the number and size of voids were increased. The permeation of gases was improved from 100,000 L m(-2) h(-1) (at 10 degrees C) to 150,000 (02), 250,000 (air), 380,000 (N-2) and 600, 000 L m(-2) h(-1) (H-2) by increasing the temperature up to 80 degrees C. This increment resulted in selectivity alteration either increment or diminishment. The selectivity was changed from 1.3 to 3.2 (H-2/O-2), 0.8-2.5 (N-2/O-2), 1.2-2.4 (H-2/air), 0.6-1.5 (N-2/air) and 2.0-1.5 (H-2/N-2). (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 114: 484-490, 2009