Abstract: The antimicrobial activity from Forsythia Suspensa leaves extract (FSLE) and its stability were studied with Staphylococcus aureus, Bacillus subtilis, and Escherichia coli as the indicator strain. The results showed that the extract had very strong antimicrobial activity, and it kept the high thermostability. The FSLE had obvious antibacterial activity on range of pH from weak acid to neutral. At greater than 30min ultraviolet radiation had slight effect on Staphylococcus aureus and Bacillus subtilis, H2O2 had obvious effect, and Na+, K+ showed a little effect on the antimicrobial activity, Ca2+, Cu2+, Fe3+ enhanced antibacterial activity of FSLE.