Five strains of Gram-positive, endospore-forming, moderately halotolerant bacteria were studied taxonomically. Four were isolated from Vietnamese fish sauce and one from the Gulf of Mexico. Phylogenetic analysis based on 16S rRNA gene sequences showed that these strains clustered within the radiation of the genus Bacillus but separately from recognized Bacillus species. DNA G+C composition of the isolates ranged from 43 to 44 mol%. Strains 15-1(T) and NRRL B-14850 showed high levels of DNA-DNA relatedness (82-100 %) to each other and to the other strains isolated here; they displayed low levels of DNA-DNA relatedness (<29 %) to the type strains of selected recognized Bacillus species. They grew in 15 % NaCl and optimally in 1 % NaCl, which is characteristic of moderately halotolerant bacteria. The isolates grew at pH 6.5 to 10.0 but not at pH 6.0. Their cell walls contained meso-diaminopimelic acid. The major isoprenoid quinone was MK-7 and the principal cellular fatty acids were anteiso-C(15 : 0), iso-C(15 : 0) and anteiso-C(17 : 0). Based on these results, the strains tested were regarded as members of a novel Bacillus species for which the name Bacillus vietnamensis sp. nov. is proposed. The type strain is 15-1(T) (=JCM 11124(T)=NRIC 0531(T)=NRRL 23890(T)).