A fastening device is disposed in one installation hole of a vehicle wheel rim to fasten the wheel rim to a wheel hub. The fastening device includes a fastening unit and a reinforcing unit. The fastening unit has an abutting portion corresponding to the installation hole and a tightening portion coaxially connected with the abutting portion. The reinforcing unit is coaxially and rotatably coupled with the fastening unit, and has a friction wall which extends radially to abut against an abutting wall of the fastening unit. The reinforcing unit is rotated and tightened along a longitudinal axis to the fastening unit through abutment of the friction wall against the abutting wall. The fastening unit and the reinforcing unit respectively have first and second threaded holes aligned with each other.