Superplastic deformation behaviour of conventional sheets of a near-α titanium alloy (Ti-2.5 Al-1.8 Mn) was studied by a step-by-step decrease of the strain rate and constant strain rate tests in a temperature range of 790–915° C. The research found that superplastic deformation is possible in a temperature range of 815–890° С and a constant strain rate range of 2× 10− 4 to 1× 10− 3 s− 1 with elongation above 300% and m-index above 0.4. Also, the research identified the optimum superplastic temperature range of 815–850° C and constant strain rate of 4× 10− 4 s− 1 which provide a maximum elongation of 600–650%. Strain hardening is accelerated by dynamic grain growth at high temperatures of 865 and 890° С. High dislocation activity is observed at superplastic flow in α-phase. Constitutive modelling of superplastic deformation behaviour is performed, and possible deformation