The guide rail assembly for a vehicle seat comprises two pairs of interhooked guide rails one being secured to the seat and the other to the floor of the vehicle. The seat rail includes a mounting member for safety belts and in the proximity of the mounting member is secured to a hook-shaped reinforcing member which engages a corresponding hook-shaped portion of a cooperating reinforcing rail which is secured to the stationary guide rail. The upper hook-shaped reinforcing member is dimensioned such as to be deformed in the case of excessive loads applied to the safety belt thus preventing the guide rails from being torn apart.