A magnetic fluid shaft-sealing device includes an outer ring for receiving a rotary shaft. A magnetic-field generating unit is mounted in an annular seal chamber of the outer ring for receiving the rotary shaft. A seal ring is mounted in the seal chamber of the outer ring and located between a magnet of the magnetic-field generating unit and an end of the outer ring. The seal ring includes inner and outer peripheries spaced in a radial direction. A lip extends from the inner periphery of the seal ring toward or away from the end of the outer ring and is at a non-parallel angle to the radial direction of the seal ring to form a seal around the rotary shaft.