<jats:title>Abstract</jats:title><jats:p>A new siderophore named tsukubachelin was isolated from an iron‐deficient culture medium of newly isolated strain Streptomyces sp. TM‐34. The chemical structure of tsukubachelin was established by the interpretation of 2D NMR and TOF‐Mass spectroscopic data. The structure of tsukubachelin consists of six amino acid residues, including three serine, and one each of <jats:italic>N</jats:italic>‐α‐methyl‐<jats:italic>N</jats:italic>‐δ‐hydroxy‐<jats:italic>N</jats:italic>‐δ‐formylornithine, <jats:italic>N</jats:italic>‐α‐methyl‐<jats:italic>N</jats:italic>‐δ‐hydroxyornithine, and cyclic <jats:italic>N</jats:italic>‐hydroxyornithine. Because the structurally related siderophore, desferri‐foroximithine, was reported to have potent angiotensin‐converting enzyme inhibition activity, the inhibitory activity of desferri‐tsukubachelin and desferri‐foroximithine were tested for structure–activity comparison. Desferri‐tsukubachelin showed 14 times more potent inhibitory activity than desferri‐foroximithine. This result indicates that desferri‐tsukubachelin may become a promising agent for angiotensin‐converting enzyme inhibition.