AZ31B magnesium alloy with initial grain size of 11.2 µm was grain refined using Equal Channel Angular Pressing (ECAP) the alloy was ECAP-processed up to 5-times at 473 K. As a result, the grains are refined to 2.1 µm after three ECAP passes, the elongation was increased to 84 % at 473 K and strain rate of 1×10-4 s-1 after ECAP up to 5-passes,. Large fracture elongations of 261% are obtained at 623 K and strain rate 2.45×10-4 s-1 for specimen made from 3 ECAR passes compared to 183% for the as received material. Also the superplastic properties of the ECAP-processed specimens were investigated at 623 K and the strain rate ranges from 2.45×10-4 s-1 to 1.2×10-3 s-1. The strain rate sensitivity were determined to be 0.33