Two strains of lactic acid bacteria were isolated from faeces of two actively racing thoroughbred horses. The isolates formed a subcluster in the Lactobacillus reuteri phylogenetic group, closely related to Lactobacillus fermentum, L. gastricus, L. ingluviei and L. mucosae, by phylogenetic analysis based on 16S rRNA gene sequences. Levels of DNA-DNA relatedness revealed that the isolates belonged to the same taxon and were genetically separated from their phylogenetic relatives. Biochemical and physiological characteristics also distinguished the isolates from their phylogenetic relatives. The isolates produced spherical or oval cells, and tetrad-like cells were rarely seen. To the best of our knowledge, this is the first report of this morphological characteristic within the genus Lactobacillus. Thus, the isolates represent an atypical novel species of the genus Lactobacillus, for which the name Lactobacillus equigenerosi sp. nov. is proposed. The type strain is NRIC 0697T (=JCM 14505T =DSM 18793T).