Magnesium alloys have attracted the interest of the modern manufacturing industry owing to their higher strength-to-weight ratios and heat conductivity than other alloys. Laser welding will be an important joining technique for magnesium alloys with their increasing applications in aerospace, aircraft, automotive, electronics, and other industries. The Nd:YAG laser beam has the reputation to be a rapid, precise, and easy process for welding of magnesium alloys. In this study, the use of an Nd:YAG laser for thin-plate AZ91 magnesium alloy welding was optimized. The welding cross section geometries were determined by optical microscopy analysis. Some important laser processing parameters (laser power, welding speed, and shielding gas flow) and their effects on the welding quality are discussed.