A sealing device (24) of a filter system (10) for filtering fluids, in particular of a motor vehicle, with a sealing ring (26) is described. The sealing ring (26) serves to seal a pipe (16), in particular a central pipe of a filter housing (12), that penetrates through a flange-sided opening (18) of an end plate (20), in particular of an end element of a filter element (14). The sealing ring (26) features a central section (58) that connects it with the end plate (20). The sealing ring (26) features in its axial direction on both sides of the central section (58) elastic sealing sections (60, 62) which cause each a reduction of the inner diameter of the sealing ring (26) compared with the central section (58). The elastic sealing sections (60, 62) extend freely flexibly and can be bent away from the central section (58) such that they can be pressed—when the pipe (16) is mounted—by means of prevailing fluid pressures—when the filter system (10) is operated—in radial direction against the exterior wall of the pipe (16).