Crude methanol extract of 9 Vietnamese plants were in vitro screened for their antibacterial activity against three common freshwater fish pathogens including Aeromonas hydrophila, Edwardsiella ictaluri, and Streptococcus agalactiae. Agar disc diffusion method was used to evaluate the antibacterial activity, then solvent extract was performed for the extracts which exhibited the strongest and a broad-spectrum antibacterial activity. Minimal inhibitory concentration (MIC) was conducted for effective plant extracts using broth dilution method. The results indicated that most of the plant extracts exhibited antibacterial propeties to at least one tested bacterium. Headache tree (Premna corymbosa), bushwillows (Combretum quadrangulare) and Celandine spider flower (Cleome chelidonii) showed a broad-spectrum antibacterial activity. The largest inhibitory zones of 35 mm and 21 mm were observed  for the extract of Premna corymbosa against E. ictaluri and S. agalactiae, respectively. E. ictaluri was found to be the most susceptible for all of the extracts while A. hydrophila was the most resistant. The MIC of effective plant extracts against tested bacteria ranged between 0.39 mg/mL and 3.125 mg/mL. The result can be considered for further investigation of the development of an alternative therapy against bacterial infection in aquaculture.