Superplasticity in an Al-6%Cu-0.45%Mg-0.4%Mn-0.16%Sc-0.12%Zr alloy subjected to intense plastic straining through equal-channel angular extrusion (ECAE) was studied in tension at strain rates ranging from 5.6×10-4 to 5.6×10-3 s-1 in the temperature interval 350-450°C. The alloy had a non-uniform microstructure with an average crystallite size of 1.2 m. The volume fraction of high-angle grain boundaries was about 57%. In spite of small crystallite size the alloy shows moderate superplastic properties. The highest elongation-to-failures of 320% appeared at a temperature of ~425°C and an initial strain rate of ~1.410-3 s-1, where the strain rate sensitivity coefficient, m, was about 0.33. The relationship between superplastic ductilities and microstructure stability is analyzed.