As an original strain, antagonistic bacteria Ata28 against tobacco brown spot was mutated by UV, DES and Microwave irradiation，and mutant strains Uv-126，Des-66，Mw-110 were tested for genetic stability. Mw-110 was obtained through the microwave irradiating，and its inhibition zone was increased 29.8% from 8.4mm to 10.9mm, and its increase of inhibition zone exceeded Uv-126, Des-66. Successively cultured eight times in the medium, heredity character of Mw-110 was stabler than Uv-126, Des-66.
