Methanol extracts of Paeonia lactiflora roots (Radix Paeaniae Lactiflora) had antibacterial activity against Bacillus subtilis. These extracts generated superoxide radicals in the B. subtilis lysate. However, the radicals were strongly detoxified by the addition of superoxide dismutase, an indication that superoxide radicals are important in the antibacterial actions of the extracts. The root extracts also showed a pivotal inhibition role in trafficking of viral glycoprotein in virusinfected baby hamster kidney (BHK) cells. The methanol extract effectively inhibited syncytium formation in a concentration-dependent, and it did not affect glycoprotein synthesis. These results suggest that oxygen radical affect the transport process of viral glycoprotein without its synthesis.