<p>A new α-pyrone, nocapyrone S (<b>1</b>), together with five known compounds (<b>2-6</b>), were isolated from the deep-sea actinomycete <i>Nocardiopsis dassonvillei</i> subsp. <i>dassonvillei</i> DSM 43111(T). Their structures were determined by spectroscopic analyses. The absolute configuration of <b>1</b> was established by quantum approaches. Cytotoxic activity of <b>1</b> was evaluated against K562, MCF-7, SGC7901, A375, Hela, and HepG2 cell lines.</p