The microstructure of a Ti--48Al alloy cooled after a solution treatment in the α-field is influenced by the cooling rate. In order to characterize the lamellar structure and to know the values of α 2 -volume fraction, width of α 2 -lamellae, and interlamellar spacing, we developed a method of measurement based on an observation of laths in the scanning electron microscope. The study revealed the heterogeneous distribution of the lamellar structure in a commercial purity Ti--48Al alloy cooled from the α-field at a rate of 35 o C/min. The evolution of α 2 -volume fraction with the cooling rate showed that the microhardness is determined by the quantity of α 2 -phase. The values of yield stress also increased and were all the less scattered as the structure became more perfectly lamellar. Yield stress and interlamellar spacing are linked by a Hall--Petch relation.