Two strains of lactic acid bacteria, designated SU 18(T) and SU 83, were isolated from silage prepared with Sudan grass [Sorghum sudanense (Piper) Stapf.]. The isolates were Gram-stain-positive, catalase-negative, facultatively anaerobic rods that did not produce gas from glucose. The isolates exhibited ≥93.5 % DNA-DNA relatedness to each other and shared the same phenotypic characteristics, which indicated that they belonged to a single species. The DNA G+C content was 58.5-59.2 mol%. On the basis of 16S rRNA gene sequence analysis, the isolates were placed in the genus Lactobacillus. Their closest phylogenetic neighbours were Lactobacillus manihotivorans JCM 12514(T) and Lactobacillus camelliae JCM 13995(T) (95.9 and 96.8 % 16S rRNA gene sequence similarity, respectively, with strain SU 18(T)). Ribotyping revealed that strain SU 18(T) was well separated from L. manihotivorans JCM 12514(T) and L. camelliae JCM 13995(T). Strain SU 18(T) exhibited ≤23.7 % DNA-DNA relatedness with its closest phylogenetic neighbours. The isolates represent a novel species in the genus Lactobacillus, for which the name Lactobacillus nasuensis sp. nov. is proposed. The type strain is SU 18(T) ( = JCM 17158(T) = CGMCC 1.10801(T)). The description of the genus Lactobacillus is also amended.