Aeromonas veronii is a kind of pathogenic microorganisms found in the intestinal tract of loach Misgurnus anguillicaudatus, and may result in 60% high mortality. Here， 57 antagonistic bacteria strains against A. veronii were isolated from the samples collected from aquaculture water, sludge and intestine of healthy and sick loaches. Their antibacterial activities were examined by cylinder plate method with TSB medium. A bacterial strain, named CMA 1, was screened from them and identified as Bacillus methylotrophicus CMA 1 by morphological observation, physiological characteristics tests, and 16S rDNA sequence analysis. The growth of CMA 1 entered into the stationary phase after being cultured for 24h ,and its antibacterial activity was up to the maximum at 36h. The crude metabolites were separated from fermentation broth through ammonium sulfate precipitation, and their antibacterial activities were examined. The results showed that the antibacterial activity of precipitate at 75% (NH4)2SO4 saturation was significantly higher. CMA 1 would be a useful probiotics in the prevention and control of fish disease caused by A. veronii.