Abstract: Flavonoids were extracted from Guanxi pomelo dropped fruits. The content of total flavonoids was up to 64.5% after recrystallization. The antibacterial effects of flavonoids extracts on Escherichia coli,Staphylococcus aureus,Bacillus subtilis,and Candida albicans were studied by turbidimetric method using rutin as comparison. Meanwhile,the eliminating ability in vitro of flavonoids extract on hydroxyl radical(·OH),diphenyl bitter hydrazine free radical (DPPH·) and superoxide anion free radical (O₂^-·) were also studied.Results showed that flavonoids extracts had certain inhibition effect on Escherichia coli,Staphylococcus aureus,Bacillus subtilis and Candida albicans,and the antibacterial rates were in the order of:Bacillus subtilis > Candida albicans > Escherichia coli > Staphylococcus aureus. In addition,The antibacterial rate increased with the increase of flavonoids extracts concentration. The half inhibitory concentrations(IC₅₀) of four kinds of the test bacterium were 2.18 mg/mL,1.7 mg/mL,4.6 mg/mL and 10.4 mg/mL,respectively,which were 100 times,10 times,10 times and 15 times that of rutin. Moreover,O₂^-·,DPPH·and·OH could be eliminated effectively by flavonoids extracts,the eliminating abilities were showed as follows:O₂^-·> DPPH·>·OH. The half inhibitory concentrations were 1.23 mg/mL,4.73 mg/mL and 11.46 mg/mL,respectively,which were 4 times,400 times and 100 times that of rutin.