Described is a device for mounting an annular flanged seal that includes a sealing ring (1) which can be inserted into an annular groove (22) of the screw-connected annular flanges (18). Said device comprises pliers which grip the sealing ring (1) between clamping jaws (2) of two facing legs (3, 4) and the jaw opening of which is adapted to the outer diameter of the sealing ring (1). In order to create advantageous design conditions, one of the two facing legs (3, 4) includes a guiding connection piece (5) for the other facing leg (3, 4) slidably mounted on the guiding connection piece (5) which extends in the direction of the jaw opening of the pliers, said other facing leg (3, 4) being clampable to the guiding connection piece (5) by a clamping mechanism (8).