Abstract The purpose of this work was to develop a methodology to establish the phase diagram of a binary gelatin/water system in order to study the elaboration process of gelatin membranes. The process involved dry-casting of gelatin solutions, temperature induced gelation (TIG) and membranes drying. The sol/gel transition was measured by rheological measurements and a novel methodology coupling thermogravimetric analyses and extensional rheology was established to determine the gel/membrane transition. By means of this process, called “TIG/dry-cast”, dense gelatin membranes were prepared. Gas permeability values for He, CO2, N2 and O2 of gelatin based films were measured for temperatures ranged between 25°C and 90°C. The relatively low permeability values (<1.5Barrer) with interesting selectivity coefficients for CO2/O2 of about 10 between 25°C and 40°C made these membranes more suitable for thin layer deposition onto porous support for gas separation applications. All these results confirmed that gelatin is a promising biobased polymer for membrane preparation. The methodology developed in this paper can be applied to other gelatin/water systems to establish their phase diagram.