Superplastic behavior of a high-strength 7475 aluminum alloy subjected to intense plastic straining through equal-channel angular extrusion (ECAE) was studied in tension at strain rates ranging from 1.4 x 10(-3) to 5.6 x 10(-2) s(-1) in the temperature interval 400-450degreesC. Microstructure of the 7475 aluminum alloy after ECAE was non-uniform. Volume fraction of fine grains with average size of about 1.2 mum was similar to60%. These grains alternate with elongated grains having longitudinal size of similar to5 mum. The highest elongation-to-failure of similar to470% was attained at a temperature of 425degreesC and an initial strain rate of 1.4 x 10(-2) s(-1) with the corresponding strain rate sensitivity coefficient, m, of 0.37. It was shown that the main feature of superplastic behavior of the ECAE processed 7475 aluminum alloy is an extensive strain-hardening at initial stages of superplastic deformation attributed to instability of microstructure.