High strain rate superplastic behavior of 5083 Al - 0.2 wt.% Sc with a grain size of similar to 0.3 mum, fabricated by equal channel angular pressing, was examined at 10(-3)similar to1 s(-1) and 673 similar to 773 K. The log (stress) - log (strain rate) relationship showed a sigmoidal behavior at 723 and 773 K. At the low ((epsilon) over dot<5x 10(-3) s(-1)) and high (5x10(-2) s(-1)<(epsilon) over dot) stain rate regions, the strain rate sensitivity (m) and activation energy (Q(t)) were 0.25 and 90 kJ/mol, respectively. At the intermediate strain rate region (5x10(-3) s(-1) <(epsilon) over dot <5x 10(-2) s(-1)), m = 0.5 and Q(t) = 60 kJ/mol. The maximum elongation to failure of 740 % was obtained at (epsilon) over dot = 1x10(-2) s(-1) and 773 K. By contrast, at 673 K, no sigmoidal behavior was observed. Instead, the mechanical data were fit into a straight line with a slope of 0.3. The deformation mechanisms were discussed in light of various standard high temperature deformation mechanisms.