The structure of bisucaberin, a new siderophore, was determined to be 1,12-dihydroxy-1,6,12,17-tetraazacyclodocosane-2,5,13,16-tetron e by spectroscopic analysis and X-ray crystallographic analysis. The molecule of bisucaberin consists of a cyclic dimer of 1-hydroxy-1,6-diazaundecane-2,5-dione moiety and is closely related to nocardamine, the trimer of the same moiety.