<jats:title>Abstract</jats:title><jats:p>Two new unusual 23‐membered macrolactones, named griseoviridins B (<jats:bold>1</jats:bold>) and C (<jats:bold>2</jats:bold>), along with the known analogue griseoviridin (<jats:bold>3</jats:bold>) were isolated from the culture of <jats:italic>Streptomyces</jats:italic> sp. IMBJ01, a terrestrial bacterium isolated from Wolong, Sichuan Province, China. The structures of <jats:bold>1</jats:bold> and <jats:bold>2</jats:bold> were elucidated on the basis of extensive spectroscopic data and their absolute configurations were determined by comparison of their CD spectra with those of compound <jats:bold>3</jats:bold>.