An antagonistic bacteria strain By33 against TMV was isolated from tobacco soils. Basing on morphological observation, physiological & biochemical test and 16S rDNA sequence analysis, By33 was identified as Bacillus amyloliquefaciens. The active substance lost most active control at 80 ℃, and was unstable in acid condition yet stable in neutral or slight alkaline condition, with resistant to proteolytic enzymes.