Recently, since the size of component becomes smaller, then the welding of thin metal sheet has been required. Besides, the flexibility of process is important according to the accessibility especially for small components. Fraunhofer Institute for Laser Technology had developed the SHADOW((R)) welding technology, in which the high speed joining with small distortion is possible using pulsed Nd:YAG laser. The possibility of high speed and high quality welding had been reported by using single-mode fiber laser. The combination of micro beam and high speed laser scanning has the advantages for thin metal sheet welding. Therefore, the characteristics of micro-welding for thin metal sheet were investigated by high speed laser scanning, in which the welding was carried out by high speed scanner system with single-mode fiber laser and pulsed Nd:YAG laser. The proper welding region was narrow by the laser beam with a large focus diameter of 160 mu m without pulse control, while a small focus diameter of 22 mu m can control the welding state widely. A small focus diameter can perform the excellent welding seam from the extreme beginning without pulse control. The penetration depth can be controlled by the energy density with a small focus diameter of 22 mu m at the energy densities less than 1 J/mm(2). Besides, the unique periodic structure appeared at the high velocity of beam scanning with a small focus diameter. Moreover, the overlap welding of 25 mu m thickness sheet can be performed regardless of small gap distance between two sheets by the laser beam with a small focus diameter of 22 mu m.