Strains of gram-negative anaerobic rods were isolated from chinchilla (Chinchilla lanigera) faeces, and three strains, ST161(T), ST33 and ST37(T), were investigated taxonomically. Based on phylogenetic analyses and specific phenotypic characteristics, the three strains were allocated to the genus Bacteroides. Phylogenetic analyses of their 16S rRNA gene sequences revealed that strain ST161(T) formed a distinct line of descent, with highest sequence similarity to strain ST33 (98.7 %) and Bacteroides oleiciplenus JCM 16102(T) (97.7 %). High levels of DNA-DNA relatedness (79-89 %) were found between strains ST161(T) and ST33, but low levels were found between strain ST161(T) and B. oleiciplenus JCM 16102(T) (33-37 %) and between strain ST33 and B. oleiciplenus JCM 16102(T) (33-37 %). These data clearly indicated that strains ST161(T) and ST33 represent a single novel species. 16S rRNA gene sequence analyses showed that strain ST37(T) also formed a distinct line of descent, with highest sequence similarity to Bacteroides acidifaciens JCM 10556(T) (96.5 %) and Bacteroides caccae JCM 9498(T) (95.6 %). Analysis of hsp60 gene sequences also supported these relationships. Based on phenotypic and phylogenetic characteristics, two novel species, Bacteroides stercorirosoris sp. nov. and Bacteroides faecichinchillae sp. nov., are thus proposed. The type strains of B. stercorirosoris and B. faecichinchillae are ST161(T) ( = JCM 17103(T) = CCUG 60872(T)) and ST37(T) ( = JCM 17102(T) = CCUG 60873(T)), respectively. The DNA G+C contents of strains ST161(T) and ST37(T) were 45.7 and 41.0 mol%, respectively.