Coral mucus covers the surface of coral and contains antibacterial substances as a first line of defense. Coral mucus not only enables the coral itself to resist disease, but also provides antibacterial agents for people. We collected mucus from a scleractinian coral (Symphyllia gigantea) at Sta. Sanya (China), then extracted the antibacterial substances using 10% glacial acetic acid with the help of antiprotease inhibitors, and tested the antibacterial activity by a terrestrial bacterium (Staphylococcus aurevs) and a marine bacterium (Vibrio anguillarum). The result showed that, there were antibacterial agents in the mucus, and their antibacterial activities were lost by treatment of the sample at 90 °C water for 10 min.