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Tensile experiments on a fine-grained single-phase Mg–Zn–Al alloy (AZ31) at 673K revealed superplastic behavior with an elongation to failure of 475% at 1×10⁻⁴s⁻¹ and non-superplastic behavior with an elongation to failure of 160% at 1×10⁻²s⁻¹; the corresponding strain rate sensitivities under these conditions were ∼0.5 and ∼0.2, respectively. Measurements indicated that the grain boundary sliding (GBS) contribution to strain ξ was ∼30% under non-superplastic conditions; there was also a significant sharpening in texture during such deformation. Under superplastic conditions, ξ was ∼50% at both low and high elongations of ∼20% and 120%; the initial texture became more random under such conditions. In non-superplastic conditions, deformation occurred under steady-state conditions without grain growth before significant flow localization whereas, under superplastic conditions, there was grain …