Abstract: Inhibition zone diameters and minimum inhibitory concentrations(MIC)of 10 phenolic compounds from mulberry(Morus alba L. )against 4 common pathogenic bacteria(Staphyloccocus aureus, Bacillus subtilis, Escherichia coli, Salmonella spp )were tested by agar diffusion and micro-dilution in order to study the antibacterial activity of mulberry. The results indicated that the monomeric compounds exhibited more effect on Gram-positive bacteria(Staphylococcus aureus, Bacillus subtilis)than Gram-negative ones(E. coli, Salmonella). The antibacterial activity of Morusin, Kuwanon E and Sanggenol A on Gram-positive bacteria were the best. Especially, the MIC of Morusin against Bacillus subtilis was below 3. 72 μmol/L. Structure-activity relationships of these compounds were also discussed. It was found that stereoisomerism, species and position of substituent had implications for their antibacterial activity. Especially, prenyl was very important for the antibacterial activity of compounds.