The use of sunflower protein isolate for the manufacturing of biodegradable materials by thermomechanical means requires a characterization of its thermal properties. After modelling of its hydration properties, DSC analysis shows a relaxation phenomenon at 60 degreesC and makes it possible, despite the changes in state of the absorbed water, to determine its glass transition temperature. The evolution of this temperature according to the water content of the samples is then modelled and compared to that of more common proteins.