A compact long-life magnetic fluid seal for sealing between a housing and a magnetically permeable rotating shaft includes an annular magnet having a closely-spaced, noncontacting relationship with the shaft to define a first gap and an annular pole piece axially abutting the magnet and having a closely-spaced, noncontacting relationship with the shaft to define a second gap. The first gap has a slightly larger radial dimension than the second gap, and the first and second gaps together define an elongated annular space for retention of a magnetic fluid. The outer edges of the pole piece and magnet inner surfaces can be rounded to limit splashing of the magnetic fliud. In another embodiment, a magnetic fluid seal includes first and second pole pieces axially abutting opposite ends of an annular magnet. The magnet has a slightly larger inside diameter than either of the pole pieces. The pole pieces and the magnet together define an elongated annular gap for retention of magnetic fluid. The seal structure permits introduction of a relatively large volume of magnetic fluid, thereby extending the seal life, while maintaining a short axial dimension.