The antibacterial activity of garlic powder against O-157 was tested by using garlic bulbs post-harvested 1 y. O-157 at 10(6-7) cfu/mL perished after incubation for 24 h with a 1% solution of garlic powder. The use of powder from fresh garlic was more effective for antibacterial activity than that from old garlic; the 1% solution of fresh garlic powder eradicating the O-157 in 6 h. The antibacterial activity was resistant to heat treatment of 100 degrees C for 20 min. The water-soluble components of garlic powder were fractionated into three fractions (Fr. 1-3) by Sephadex G-100 column chromatography, among which Fr. 3 showed antibacterial activity against O-157 but the other fractions were scarce in activity. The antibacterial activity was also shown against other types of pathogenic bacteria such as methicillin-resistant Staphylococcus aureus (MRSA), Salmonella enteritidis, and Candida albicans. Thus, the practical use of garlic powder is expected to prevent bacteria-caused food poisoning.