Four strains (NUM 1903(T), NUM 1904, NUM 1912 and NUM 1925) that were obligately anaerobic, pigmented, Gram-negative-staining rods were isolated from the oral cavity of donkeys. These strains were analysed using the Rapid ID 32A, API 20A and API ZYM systems, by DNA-DNA hybridization with other related species and by 16S rRNA gene sequencing. 16S rRNA gene sequence analysis showed that each of the new isolates was a member of the genus Prevotella and related to Prevotella multiformis PPPA21(T), showing about 93 % sequence similarity. Based on phylogenetic and phenotypic evidence, it is proposed that the four strains are representatives of a novel species, for which the name Prevotella dentasini sp. nov. is proposed. The type strain is NUM 1903(T) (=JCM 15908(T)=DSM 22229(T)).