Ethanol extract of puchiin was assayed for its antimicrobial properties. The results showed that puchiin extract had antibacterial activities. Further more study revealed that the puchiin extract had stronger antimicrobial activity against the tested bacterial lstaphylococcus aureus and Escherichia coli than that of potassium sorbate. Extract of puchiin was also studied for its stability to acid, alkali, temperature, ultraviolet and metal ions. The results showed that the extract was very stable to acid and alkali. After treated with alkali, the extract still showed high antibacterial activity. Ultraviolet and metal ions also had little effect on the antibacterial activity of puchiin extract. Only high temperature up to 121℃ with half an hour`s treatment showed a little effect on extract antimicrobial activity. The UV radiation and metalions (Na+, K+, Ca2+, Fe2+, Fe3+) showed also little effect on extract antimicrobial activity.