In order to evaluate the weldability of a melt-spun Ni-based metallic glass foil with a thickness of 25 urn, bead-on-plate laser welding was carried out at different welding speeds from 2 to 12 m/min using a diode laser beam with a constant laser power of 26 W and wavelength of 808 nm. A sound weld bead, while maintaining the amorphous state, was successfully obtained at a high welding speed of 12 m/min; under these conditions, the weld bead consisted of an amorphous matrix with a very small amount of nanocrystals with a mean diameter of 14 nm. The hardness was almost the same as that of the base metal (740 HV), and the mean tensile strength of the weld bead was 1312 MPa, which is 56% of that of the base metal. At a lower welding speed of less than 6 m/min, a fusion zone appeared in the central zone of the weld bead consisting of the amorphous matrix with comparably large crystals with mean diameter of 170 nm. Further, the heat-affected zones adjacent to the fusion zone consisted of a completely crystallized structure with a high hardness of around 1200 HV, which caused a low joint strength or weld cracking due to the brittleness of crystallization or structural relaxation.