A new isoflavone derivative was isolated from Rosa damascena by using various chromatographic techniques including silica gel, Sephadex LH-20, and preparative RP-HPLC separation. Its structure was identified as 4'-hydroxy-7-(3-hydroxypropanoyl)-6-methoxy-isoflavone using combined examinations of their UV, IR, MS, and NMR spectroscopic data. Biological activity test showed that this compound showed prominent antibacterial activity with MIC₉₀ value of (46±4) mg·L⁻¹ for methicillin resistant Staphylococcus aureus(MRSA) strain. This value is close to that of levofloxacin [with MIC₉₀ value (53±5) mg·L⁻¹].