A magnetic shaft seal has a sealing ring (1) made of permanently magnetized plastics that surrounds a rotatable shaft (4) and is provided on the side facing the shaft (4) with an annular recess (2). The areas located on both sides of this recess (2) act as ring poles (3) and form each with the shaft surface (4) a gap filled with ferrofluid (6). At least one of the front faces of the sealing ring (1) is covered with a protective layer (11) which prevents foreign matter to come out from the surface of the sealing device covered with the protective layer (11).
