Abstract: There is provided an antibiotic composition including Eisenia bicyclis-derived phlorotannin compound, in which the antibiotic composition includes a phlorotannin compound selected from 7-phloroeckol, fucofuroeckol-A, and dioxinodehydroeckol, or mixture thereof, which are derived from Eisenia bicyclis, as an effective component. The compounds described above exhibit an antibiotic activity against an antibiotic-resistant bacterium. In addition, the compound described above can exhibit a synergetic effect by using in combination with ?-lactam-based antibiotic composition by recovering an antibiotic activity of ?-lactam-based antibiotic, such as ampicillin, penicillin, and oxacillin against MRSA.