Abstract: The antimicrobial activities of the ethanolic extract of A. julibrissin Durazz. bark against four common microorganisms were evaluated using paper disc method and mycelial growth inhibition method. The results showed that the ethanolic extract had a minimal inhibitory concentration (MIC) of 20mg/mL against Staphylococcus aureus and a median effective concentration (EC50) of 12.43mg/mL against Aspergillus niger. These results indicated that the antimicrobial activity of the ethanolic extract against A. niger was higher than that against three other microorganisms. Then the four phases of the extract were tested against A. niger using mycelial growth inhibition method. The n-butanol phase was the most effective against A. niger among the four phases and its EC50 was 7.68mg/mL. In conclusion, the bioactive constituents were mainly in the n-butanol phase and these results provided people with great value and potential in tapping natural food preservatives.