Four strains isolated from chicken small intestine and strains JCM 1038 and JCM 1039 (designated as Lactobacillus acidophilus) were characterized by phenotypic and molecular taxonomic methods. They were Gram-positive, catalase-negative, facultatively anaerobic rods that did not produce gas from glucose. These strains had similar phenotypic characteristics and exhibited intergroup DNA relatedness values of >77 %, indicating that they comprised a single species. The 16S rRNA gene sequence of a representative strain, JCM 1039(T) (designated as type strain in this study), was determined and aligned with those of other Lactobacillus species. JCM 1039(T) was placed in the Lactobacillus delbrueckii cluster of the genus Lactobacillus on the basis of phylogenetic analysis and formed an independent cluster that was distinct from its closest neighbours, Lactobacillus amylovorus, Lactobacillus crispatus, Lactobacillus gallinarum, L. acidophilus and Lactobacillus helveticus. Results of DNA-DNA hybridization experiments and whole-cell protein profiles clearly indicated that these strains represent a novel Lactobacillus species, for which the name Lactobacillus kitasatonis sp. nov. is proposed; the type strain of this species is JCM 1039(T).