Abstract Zobellia galactanivorans has been reported as a seaweed-associated or marine-derived species with largely unknown secondary metabolites. The combination of bioinformatic analysis and MS- and bioactivity guided separation led to the isolation of a new antibiotically active dialkylresorcin from the marine bacterium Z. galactanivorans. The antibiotic profile of the new dialkylresorcin zobelliphol (1) was investigated and compared with related and naturally occurring dialkyresorcins (i.e., stemphol (2) and 4-butyl-3,5-dihydroxybenzoic acid (3)) from the marine-derived fungus Stemphylium globuliferum. Bacterial reporter strain assays provided insights into the mode of action of this antibiotic compound class. We identified an interference with bacterial DNA biosynthesis for the dialkylresorcin derivative 1. In addition, the putative biosynthetic gene cluster corresponding to production of 1 was identified and a biosynthetic hypothesis was deduced.