Pancreatic lipase is a potential therapeutic target for the treatment of diet‐induced obesity in humans. In an ongoing search for new pancreatic lipase inhibitors from natural sources, a methanolic extract of marine brown algae, Eisenia bicyclis, showed a significant inhibitory effect against pancreatic lipase. Bioassay‐guided isolation of this methanolic extract using a pancreatic lipase inhibitory assay led to the isolation and identification of six known phlorotannins: eckol (1), fucofuroeckol A (2), 7‐phloroeckol (3), dioxindehydroeckol (4), phlorofucofuroeckol A (5), and dieckol (6). The structures were established on the basis of nuclear magnetic resonance and mass spectrometry spectroscopic data interpretation. Among the isolated phloroglucinol polymers, compounds 2 and 3 showed potent inhibitory effects on pancreatic lipase with IC50 values ranging from 37.2 ± 2.3 to 12.7 ± 1.0 μM, respectively. Copyright © 2012 John Wiley & Sons, Ltd.