The plasticizing effect on wheat gluten of a series of saturated fatty acids with different carbon chain length (from 6 to 10 carbons) was investigated. Plasticized materials were obtained by mixing in a counter-rotating batch mixer. The wheat gluten plasticization with the saturated fatty acids was shown to be thermodependent. Differential scanning calorimetry enabled the determination of the compatibility limits between wheat gluten and the fatty acids. Plasticizing effect, as judged from the shift of the temperature of the glass to rubbery transition, was determined by dynamic mechanical thermal analysis. As results showed a series effect on several times, it was thus possible to approximate the plasticizing effect of the different saturated fatty acids with a unique Couchman-Karasz equation. The molecular size distribution of the plasticized gluten was analyzed by size-exclusion high performance liquid chromatography (SE-HPLC). Mixing of plasticized wheat gluten induced variable and complex changes in the protein size distribution and resulted in a predominant polymerization, indicating a gluten reactivity in the presence of the fatty acids. The water vapor permeability of films obtained by pressure molding from the mixed plasticized samples showed improved barrier properties in comparison with films from wheat gluten plasticized with glycerol. The use of saturated fatty acids open thus new ways for the plasticization and the improvement of properties of gluten based biodegradable plastics.