Magnesium alloys are potentially useful as structural materials due to their higher strength/weight ratio, heat conductivity and recyclability compared to other alloys. These alloys have attracted the interest of modern manufacturing, such as the automobile, computer, communication and consumer electronic appliances industries. This study is related to the laser weldability of AZ31 magnesium alloy, an all-purpose wrought alloy with good strength and ductility. The effects of welding conditions on the weldability of butt joints were examined in more detail. In addition, the mechanical properties of butt-welded joints were investigated by tensile and hardness tests. On the other hand, because magnesium is sensitive in an oxidation environment, the effects of shielding conditions were examined by controlling the flow rate of the front and back shielding gas. As a result of this study, optimal conditions without weld defects were obtained. Consequently, a superior weld with nearly the equivalent strength and the half elongation of the base metal was obtained. The weldability, particularly the weld morphology, was clearly affected by the shielding conditions.