Magnesium alloys have attracted the interest of 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 a reputation for rapid, precise and easy operation in welding of magnesium. In this study the use of an Nd:YAG laser for thin plate magnesium alloy butt welding was optimized. Some important laser processing parameters and their effects on weld quality are discussed. The microstructure and metallurgical defects encountered in laser welding of magnesium alloys, such as porosity, welding cross sections geometry etc. were determined by optic microscopy. The welding parameters (the shielding gas, convey speed of work piece, laser focal position, pulse frequency, and pulse waveform governing the laser beam in thin plate butt welding were evaluated by gometric parameters.