In order to find therapeutic agents for porcine pneumonia, we screened far antibacterial activities of methanol extracts of 81 higher plants against four pathogenic microorganisms of Heamophilus parasuis, Pasteurella multocida, Actinobacillus pleuropneumonia, and Bordetella bronchiseptica, and found the bark of Cinnamomi cortex showed potent activities. Since this was inexpensive, we purified active compounds from it. The structures of the final active fractions were obtained through an activity-guided fractionation and their antibacterial activities are reported here.