Abstract: 【Objective】The antibacterial activity of twenty traditional Chinese medicines against Actinobacillus pleuropneumoniae in vitro was evaluated in this study. 【Method】Twenty traditional Chinese medicines like Fructus mume were extracted by ethanol reflux extraction,water decoction and ultrasonic wave. Minimal inhibitory concentrations(MICs) of twenty traditional Chinese medicines against A. pleuropneumoniae were determined by the macrodilution broth method. The joint antimicrobial activity of some traditional Chinese medicines was evaluated in vitro.【Result and conclusion】The results showed that the MICs of the extract obtained from F. mume, Rhizoma coptidis, Terminalia chebula, Cortex fraxini, Sanguisorbae officinalis and Polygonum cuspidatum against A. pleuropneumoniae ranged from 6.25 to 50.00 mg/mL. MICs of the extract obtained from Isatis indigotica, Artemisia capillaris, Glycyrrhiza uralensis and Dictamnus dasycarpus ranged from 50.00 to 100.00 mg/mL. MICs of the extract obtained from Phellodendron amurense, Eucommia ulmoides, Lonicera japonica, Bupleurum chinense, Taraxacum mongolicum, Baphicacanthus cusia, Gardenia jasminoides and Astragalus membranaceus were higher than 100.00 mg/mL. The results of joint bacteriostatic test showed that the fractional inhibitory concentration index (FICI) of the pairwise combination of F. mume, R. coptidis, Te. chebula and Po. cuspidatum was lower than or equal to 1, and FICI of C. fraxini with Po. cuspidatum and F. mume was higher than 2. The F. mume, R. coptidis, Te. chebula, Po. cuspidatum, C. fraxini and S. officinalis had a good antimicrobial activity. The pairwise combination of F. mume, R. coptidis, Te. chebula and Po. cuspidatum showed an enhanced or additive synergy action, and C. fraxini showed antagonistic action with F. mume and Po. cuspidatum, respectively.