The antibacterial activity of garlic powder was examined against Bacillus anthracis using agar plate cultivation and test tube methods. On the agar plate test, 1-5% garlic powder inhibited the growth of B. anthracis and Escherichia coli O 157 used as references. A 1% water solution of garlic powder in the test tube method killed B. anthracis at 10⁷ cfu/mL within 3h of treatment at room temperature. A number of intestinal bacteria in a BALB/c mouse decreased after the oral administration of 1 mL of 1% garlic powder solution once a day for 3 d. These results suggest that the oral administration of garlic powder is effective against pathogenic bacteria invasion into the intestine as an infection.