This study was designed to identify the effects of Reynoutria Japonica on antibacterial activity aganist Bordetella pertussis ATCC 9797 which is cause of whooping cough. The ethanol- and water-extracts of more than 80 oriental herbal medicine were Investigated by Kirby -Bauer method to determine their inhibitory effects on growth of B. pertussis ATCC 9797 in vitro. For that Reynoutria Japonica was selected. The ethanol-soluble extract of Reynoutria Japonica showed relatively high antivacterial activity against B. pertussis ATCC 9797. However, the water-soluble extract of Reynoutria Japonica showed no antibacterial activity. The ethanolic extract was further fractionated with organic solvents such as hexane, chloroform, and ethyl acetate, in that order. Among the fraction tested, the chloroform fraction showed the highest antibacterial activity when the ethanol-soluble extract of Reynoutria Japonica minial inhibitory concentration(MIC) was $25{mu}g/m{ell}l$. Results support a role far Reynoutria Japonica in inhibiting the cell growth of B. pertussis ATCC 9797, but further experimentation is required.