Glycoglycerolipids were isolated from seaweed-associated marine actinomycete strain PK206-15, which was identified as Streptomyces coelescens based on 16S rDNA sequence analysis. The compounds were isolated by silica gel chromatography and high performance liquid chromatography. The structures were analyzed by nuclear magnetic resonance, high resolution-electrospray ionization-mass spectrometry, and methanolysis. The compounds were identified as 2R-1,2-di-12-methylhexadecanoic acid-3-O-[β-D-galactopyranosyl-(1''-6')-O-β-D-galactopyranosyl]-glycerol, 2R-1-12-methylhexadecanoic acid-2-hydroxyl-3-O-[β-D-galactopyranosyl-(1''-6')-O-β-D-galactopyranosyl]-gly cerol, 2R-1,2-di-12-methylhexadecanoic acid-3-O-β-D-galactopyranosyl-glycerol, and 2R-1,2-di-14-methylhexadecanoic acid-3-O-β-D-galactopyranosyl-glycerol. These were active against the following fouling organisms: zoospores of Ulva pertusa, the diatom Navicula annexa, the mussel Mytilus edulis, and fouling bacteria with an EC(50) range of 0.005-0.2 µg/mL.