An investigation on CO2laser welding of cast nickel-base superalloy has been carried out. The effects of the main parameters, including the laser power, the welding speed, the position of the focal point and the direction of plasma-supressing gas on the depth and width of the bead were studied. The mechanism of hot-cracking in the weld metal and the heat-affect-zone (HAZ) was investigated while the methods to reduce the cracking susceptibiliy were discussed. The results show that a defects-free joint with high tensile strength can be obtained when using proper laser welding parameters.