Flavonoids have biofunctional effects as antioxidant and antimicrobial agents. The objective of this study was to evaluate the bactericidal activity and antilipopolysaccharide (LPS) effects of flavonoids on Escherichia coli O157:H7. The effects of flavonoids on the growth of E. coli O157:H7 were bacteriostatic rather than bactericidal at concentrations below 200 ${mu}m$, and there was no significant difference among the flavonoids tested (p<0.05). LPS production in E. coli O157:H7 treated with 200 ${mu}m$ quercetin and naringenin decreased by 34.06${pm}$1.03 and 19.90${pm}$1.51%, respectively, relative to the control (no flavonoid). Luteolin, genkwanin, hesperetin, and apigenin caused decreases in LPS production of 69.85${pm}$1.03, 61.18${pm}$1.15, 60.74${pm}$1.10, and 58.93${pm}$0.98%, respectively, relative to the control. Based on these results, luteolin had the greater inhibitory effect on LPS production by E. coli O157:H7 than other flavonoids tested in this study.