Loloatins A (1) to D (4), a family of new cyclic decapeptide antibiotics, have been isolated from laboratory cultures of a tropical marine bacterium recovered from the Great Barrier Reef in Papua New Guinea. The structures of loloatins A-D were elucidated via a combination of spectroscopic analyses and chemical degradation. Loloatins A-D exhibit in vitro antimicrobial activity against methicillin-resistant Staphyloccoccus aureus, vancomycin-resistant enterococci, and drug-resistant Streptococcus pneumoniae.