A wide range of superplastic materials were investigated for their high temperature flow property characteristics. Depending on the ranges of strain rates, temperatures and grain sizes, there appear 2–3 regimes of stress–strain rate relationship, with distinct values of strain rate sensitivity index, activation energy for deformation and grain size exponent. These parameters of constitutive relationship are significantly influenced by concurrent microstructure evolution, which includes grain growth, grain refinement, dislocation dynamics, texture modification, twinning and cavity formation. An attempt was made to evaluate the contribution of such changes to modify the constitutive relationship for high temperature deformation. © 2015, The Indian Institute of Metals - IIM.