Fifty strains of non2pathogenic bacteria were isolated from tobacco rhizospheric soil, stems and leaves of tobacco, cucumber, tomato and mulberry plants. The biological inhibitions of the strains were determinated under culture conditions.The results showed that the non2plthogenic bacteria were inhibitive to Alternaria alternata. Among the fifty strains, the in hibition of the strains isolated from tobacco rhizospheric soil was the strongest .After treated by the antagonists, the formation appeared and growth of myceliumof Alternaria alternata was influnced. The brown spot was controlled efficiently after treated by the antagonists (BS5 and BS6) 1