Industrial application of magnesium alloys has increased significantly recently. However, wrought magnesium alloys still have a lot of technical challenges to be solved for more applications. First of all, low formability of wrought alloys should be improved by optimizing the processing variables. In the present study, the effect of process variables such as forging temperature and forging speed were investigated to forgeability of magnesium alloy. To understand the effect of process variables more specifically, both numerical and experimental works have been carried out on the model which contains upsetting geometry. Forgeability of AZ31 alloy was found to depend more on the forging speed rather than temperature. Forged sample showed a significant activity of twinning, which was found to be closely related with flow uniformity.