We have been attempting for some time to discover a compound evidencing antibacterial activity against methicillin-resistant Staphylococcus aureus (MRSA). The dieckol isolated from Ecklonia stolonifera has been shown to exhibit antibacterial activity against methicillin-susceptible S. aureus (MSSA) and MRSA. The minimum inhibitory concentrations (MICs) of dieckol were determined in a range of 32 to $64{mu}g$/mL against standard MSSA and MRSA strains. Furthermore, dieckol clearly reversed the high-level ampicillin and penicillin resistance of MRSA. The MICs of ampicillin against two standard strains of MRSA were dramatically reduced from 512 to $0.5{mu}g$/mL in combination with 1/4 MIC of dieckol ($16{mu}g$/mL). The fractional inhibitory concentration (FIC) indices of ampicillin and penicillin were measured from 0.066 to 0.266 in combination with 8 or $16{mu}g$/mL of dieckol against all tested MRSA strains, thereby suggesting that dieckol-ampicillin or dieckol-penicillin combinations exert a synergistic effect against MRSA. The results of this study indicate that dieckol, administered in combination with $eta$-lactams, may prove effective in the treatment of MRSA infections. Our finding may also contribute to the development of an alternative phytotherapeutic anti-MRSA agent.