The minimum inhibitory concentration(MIC)of sophoridine ,sophoramine,matrine,cytosine,oxymatrine and the total alkaloids of Sophora alopecuroides L.on bacterial strains,Escherichia coli,Enterobacter aerogenes ,Proteus vulgaris,Bacillus subtilis,Staphylococcus epidermidis was tested.The results shown that the five alkaloids and the total alkaloids of S.alopecuroid es significantly inhibited grouth of the five environmental bacterial strains. MIC of the five alkaloids on the five environmental bacterial strains were betwe en 2×10 -2 mol/L and 5×10 -2 mol/L,except 5×10 -3 mol/L for cytosine on P.vulgaris,.However,MIC of the total alkaloids of S.alopecuro ides on the five environmental bacterial strains were significantly lower than that of the five alkaloids,in which MIC on E.coli and B.subtilis reache d 5×10 -3 mol/L.Value of developing alkaloid products applied in controll ing agricultural and forest bacterial disease and medicine,defensive effects of quinolizidine alkaloids in chemical ecology of plants were discussed in connecti on with concentration and distribution of quinolizidine alkaloids in plants.