Porcine pneumonia is caused by Pasturella multiocida and Actinobacillus pleuropneumoniae. To identify a potent drug for antipneumonia therapy, several herbal compounds showing antibacterial effects were screened, and it was found that a methanol extract of Coptidis rhizoma root stem exhibited activity against both pneumonia-causing bacteria. Using an activity-guided fragmentation procedure, an isoquinoline alkaloid was isolated which would be responsible for the antibacterial activities against P. multocida and A. pleuropneumoniae.