Abstract: A sealing device for a ship's propeller shaft installed around the propeller shaft in which longitudinally spaced annular iron pole blocks, and circularly spaced permanent magnets fixed between the blocks are mounted in a cylindrical housing surrounding the propeller shaft, and a magnetic fluid fills gaps between the magnets and the annular iron pole blocks and either a liner mounted about the shaft or the shaft itself. The magnetic fluid serves as a sealant and completes a magnetic circuit which maintains a well defined thickness of magnetic fluid sealant and a high pressure seal even under great mechanical stress, thereby minimizing frictional power loss and wear to the propeller shaft or sleeves which are conventionally shrink-fitted thereto.