Abstract: In order to improve decomposition efficiency of organic nitrogen in organic fertilizer and meet the nitrogen requirement of tobacco at the early growth stage, five ammonifying bacterial strains were isolated and purified from tobacco-planted soil in Guizhou using ammoniated bacterium medium. The NH₄⁺-N concentrations in ammoniated medium of five strains were between 297 mg/L and 460 mg/L by the measurement of Nessler's reagent method. Two ammonifying strains AMM-2 and AMM-5, with the highest ammonifying ability were identified as Bacillus toyonensis and Bacillus mobilis, respectively, based on the morphological characteristics, physiological and biochemical identification, 16S rRNA gene sequencing and phylogenetic tree analysis. After incubation for 48 h at 30℃, the NH₄⁺-N concentrations of AMM-2 and AMM-5 in ammoniated medium (pH 7.0) were 514 mg/L and 505 mg/L, respectively. Good ammonifying abilities of the two ammonifying strains were observed under the condition of pH 4.0-10.0 and temperature 25-30℃, respectively. Comparing with AMM-2, AMM-5 showed the wider temperature adaptation and higher salt tolerance. The two Bacillus strains with high organic nitrogen decomposition ability, obtained in this study could provide desirable strain resources for enhancing manurial effect of organic fertilizer.