Gymnorrhizol (1), an unusual novel macrocyclic polydisulfide possessing an unprecedented carbon skeleton, characterized by a 15-membered macrocycle that composed of three repeated 1,3-dimercaptopropan-2-ol units, has been isolated from the Chinese mangrove Bruguiera gymnorrhiza and its structure was determined by extensive spectroscopic studies. A suggestion is made as to its biogenetic origin.