The selecting of proper welding process for aluminum end-capping of KMRR nuclear fuel elements is considered important in respect to the soundness of weldments and the improvement of the performance of nuclear fuels during the operation in reactor. The aluminum end-caps of KMRR nuclear fuels are welded and sealed up circumferentially, connecting end-capping and U-Si-Al fuel rod core. This study is to investigate the characteristics of the laser welded specimen and make some samples for the end-cap welding of KMRR nuclear fuels. Also, the materials principles and theories for the laser welding of aluminum were analyzed and reviewed. In order to prevent aluminum materials from the weld defects, it is required that laser power density is slightly higher than that of the threshold for the plasma generation. Especially it can be also seen that the helium gas is more effective than argon gas to decrease porosity. (Athor).