<jats:title>Abstract</jats:title><jats:p>Echinosporamicin (<jats:bold>1</jats:bold>), a novel antibiotic containing an aromatic polycyclic system and a piperazinone moiety, was isolated from the fermentation broth of a new strain of <jats:italic>Micromonospora echinospora</jats:italic> subspecies <jats:italic>echinospora, LL</jats:italic>‐P175. The structure of this compound was determined by spectroscopic analysis by using variable‐temperature NMR techniques. Compound <jats:bold>1</jats:bold> exhibited potent activity against methicillin‐resistant <jats:italic>Staphylococci</jats:italic> and vancomycin‐resistant <jats:italic>Enterococci</jats:italic> strains. The methyl, ethyl, and benzyl esters showed improved antibacterial activity against <jats:italic>Streptococci.</jats:italic>