Punica granatum (P. granatum) Linn. pericarp has been commonly employed as a crude drug in Thai traditional medicines for the treatment of diarrhea. The antibacterial activity of extracts from P. granatum pericarp against different strains of enterohemorrhagic Escherichia coli (E. coli) O157 : H7 and other strains of enterohemorrhagic E. coli were investigated. Successive chloroform, 95% ethanol, and water extracts of the plant were examined. The ethanolic extract was found to be the most effective against all the strains examined. Both the ethyl acetate and n-butanol fractions of P. granatum pericarp were demonstrated to have high activity with the highest minimal inhibitory concentration (MIC) and minimal bactericidal concentration (MBC) values of 0.05 and 0.05 and 0.39 and 0.19 mg/ml, respectively. The inhibitory effects of both fractions on the production of verocytotoxin (VT)1 and VT2 by enterohemorrhagic E. coli O157 : H7 was observed at very low concentrations of 1/10 of the MIC value (0.05-0.09 mg/ml, respectively). Phytochemical screening of the ethanolic extracts demonstrated that they contain flavonoids, sterols, triterpenes, phenols, and tannins. Our findings suggest that an appropriate bioactive compound may be developed from P. granatum pericarp as alternative treatment for this E. coli O157 : H7 infection. The crude plant may also be administered to prevent VT production in the human intestine to solve the problem of subinhibitory effects from the use of antibiotics.