Abstract: The microstructure and grain misorientation of the AZ31 magnesium alloy sheet during extrusion and rolling were investigated.The results show that the size and misorientation distribution of the middle and marginal grains of the extruded AZ31 magnesium alloy cast ingot had a great disparity.Small angle grain boundaries and no twin were found after extrusion.After rolling,both the twins and small angle grain boundaries were observed and increased with the increase of the reduction.The misorientation decreased gradually with the increase of the reduction.The deformed structure including twins disappeared after annealing and homogenous fine equiaxed grains were formed.Small angle boundaries reduced after annealing,and the grain misorientation distributed at nearly 30 degrees.