Effects of grain size on room temperature (RT) deformation behavior of superplastic Zn-22Al alloy under uniaxial and biaxial loading conditions were investigated. Two step equal channel angular pressing.(ECAP) and subsequent annealing processes were applied to the alloy in order to obtain microstructures with various grain sizes ranging from submicron to micron sizes. Grain size of 200 nm was achieved after ECAP of the alloy, and it was increased up to similar to 2.60 mu m by annealing at 250 degrees C for different time periods. Changes in deformation behaviors of the alloy with various grain sizes were found to be in good agreement under the uniaxial tensile and biaxial Erichsen test conditions. Increasing grain size decreased both the maximum elongation under uniaxial deformation and limiting dome height (LDH) under biaxial deformation. The high elongation to failure and LDH values for the samples with submicron grain size were attributed to their high strain rate sensitivity. (C) 2016 Elsevier B.V. All rights reserved.