Although in late years, magnesium has been paid attention to for its lightweight to solve the global environmental problem such as global warming, it has poor plastic formability at room temperature because of its crystal structure of hcp and texture on basal plane. In this study, firstly an AZ31 magnesium alloy extrusion has been subjected to a grain refinement treatment consisting of cold rolling and subsequent annealing. When the specimen is cold-rolled, rolling direction was rotated from the extrusion direction by 0°, 45°and 90°. Secondly the formability of the specimens was assessed by means of hydrolytic bulge test. It was found that the grain refinement became more marked and texture became more random when the angle between the extrusion direction and the cold-rolling direction decreased. As a result, the bulge formability was best in when the angle was 0°.