A fastening device for a low-profile fuses of vehicle, which can achieve simple and robust coupling of the low-profile fuse while enabling the fuse to be easily connected to or disconnected from a vehicular junction box, is disclosed. The fastening device serves to connect or disconnect the low-profile fuse to or from the junction box via upward/downward movement thereof while maintaining coupling between the low-profile fuse and the junction box, and includes a socket integrally formed at an upper surface of the junction box and having plug coupling recesses and a fuse connecting recess indented in the upper surface of the junction box, terminals being disposed inside the fuse connecting recess so as to be exposed to the outside, and a plug vertically movably coupled in the socket while being coupled laterally with the low-profile fuse to enable connection or disconnection between the low-profile fuse and the terminals.