The ability to develop superplastic properties in a two phase material depends mainly on three physical features : the volume fraction of the phases, their size (and morphology) and their composition (associated with their crystallographic structure). All these parameters are functions of the temperature of deformation. Therefore, their variation with temperature is required to determine the temperature domain in which superplastic properties can be expected a nd then to investigate the mechanisms of deformation induced in the superplastic regime. The material investigated in this study is an industrial Ti3Al based alloy, to be formed by superplastic forming. From microstructural characterization of the material in as-received conditions, it is concluded that superplastic properties can be achieved with the provided microstructure. Microstructural transformation (variations in phase compositions, grain sizes and crystallographic structure) associated with annealing in the temperature range 890-1070 degrees C was investigated. The law of variation with temperature of phase volume fractions was determined by two independent methods.