<jats:title>Abstract</jats:title><jats:p>Borrelidins M−O (<jats:bold>1</jats:bold>–<jats:bold>3</jats:bold>), along with four previously known family members (<jats:bold>4</jats:bold>–<jats:bold>7</jats:bold>), were isolated from marine pulmonated mollusks <jats:italic>Onchidium</jats:italic> sp. associated <jats:italic>Streptomyces olivaceus</jats:italic> SCSIO LO13. The structures of <jats:bold>1</jats:bold>–<jats:bold>3</jats:bold> were elucidated by extensive spectral analyses of HR‐ESI‐MS, 1D and 2D NMR data. In addition, the cytotoxic and antibacterial activities of <jats:bold>1</jats:bold>–<jats:bold>7</jats:bold> were evaluated enabling us to propose some tentative structure‐activity relationships (SARs), especially those involving modifications at C(22) and the moieties at C(7) and C(8) of the borrelidin scaffold.