Methicillin-resistant <i>Staphylococcus aureus</i> (MRSA) infections are well-known as a significant global health challenge. In this study, twenty-two congeners of the natural antibiotic rhodomyrtosone B (RDSB) were synthesized with the aim of specifically enhancing the structural diversity through modifying the pendant acyl moiety. The structure-activity relationship study against various MRSA strains revealed that a suitable hydrophobic acyl tail in the phloroglucinol scaffold is a prerequisite for antibacterial activity. Notably, RDSB analogue <b>11k</b> was identified as a promising lead compound with significant <i>in vitro</i> and <i>in vivo</i> antibacterial activities against a panel of hospital mortality-relevant MRSA strains. Moreover, compound <b>11k</b> possessed other potent advantages, including breadth of the antibacterial spectrum, rapidity of bactericidal action, and excellent membrane selectivity. The mode of action study of compound <b>11k</b> at the biophysical and morphology levels disclosed that <b>11k</b> exerted its MRSA bactericidal action by membrane superpolarization resulting in cell lysis and membrane disruption. Collectively, the presented results indicate that the novel modified RDSB analogue <b>11k</b> warrants further exploration as a promising candidate for the treatment of MRSA infections.