Equal channel angular pressing was used to process an AZ31B magnesium alloy (nominally Mg-3Al-1Zn in wt%) at temperatures decreasing from 200 to 150 A degrees C. The resulting microstructure was characterized by electron backscattered diffraction to reveal the role of low-angle grain boundaries in grain refinement. It was found that low-angle grain boundaries with misorientation angles lower than 5A degrees are surrounded by regions of increased strain gradients, which can stimulate the generation of non-basal slip dislocations during the equal channel angular pressing at temperatures of approximately 150 A degrees C. The strain gradients in the vicinity of the grain boundaries with misorientation angles in the range of 5A degrees-10A degrees were less frequent or were completely absent for high-angle grain boundaries with misorientation angles higher than 10A degrees. This article also discusses the importance of low-angle grain boundaries for the generation of non-basal aOE (c) c+a > dislocations needed for successful equal channel angular pressing of AZ31B at temperature of 150 A degrees C.