Three groups of Gram-stain-negative, obligately anaerobic, rod or coccoid-shaped bacteria, which were phylogenetically assigned in the genus Alistipes belonging to the family Rikenellaceae in the phylum Bacteroidetes, were isolated from the faecal samples of healthy Japanese humans. Group I (strains 5CBH24T and 6CPBBH3) showed highest 16S rRNA gene sequence similarity to 'Alistipes obesi' ph8T (99.73 %). Group II (strain 5CPEGH6T) was related to Alistipes shahii WAL 8301T (96.82 %). Ten strains of group III (3BBH6T, 5CPYCFAH4, 5NYCFAH2 and others) were related to Alistipes onderdonkii DSM 19147T (98.96 %). Group I could be differentiated from other strains by the ability to hydrolyse aesculin and the lack of catalase activity. Strain 5CPEGH6T could be differentiated from A. shahii JCM 16773T by the inability to hydrolyse aesculin and the lack of catalase activity, and so on. Phenotypic characteristics of group III were similar to those of A. onderdonkii JCM 16771T. Strains 5CBH24T, 6CPBBH3 and 'A. obesi' ph8T shared 98.8-98.9 % average nucleotide identity (ANI) with each other. In addition, the in silico DNA-DNA hybridization (DDH) values among three strains were 86.7-89.4 %. Strain 5CPEGH6T showed relatively low values (≤ 84.4 % for ANI ; ≤26.2 % for DDH) with other strains. Three strains in the group III (3BBH6T, 5CPYCFAH4 and 5NYCFAH2) shared 97.9-99.9% ANI with each other. These three strains showed 96.9-97.3 % ANI with A. onderdonkii DSM 19147T. The DDH values of strains 3BBH6T, 5CPYCFAH4 and 5NYCFAH2 among themselves were 80.5-99.8 %, while those compared to A. onderdonkii DSM 19147T were 71.0-73.4 %. On the basis of the collected data, three novel species, Alistipes communis sp. nov. (5CBH24T=JCM 32850T=DSM 108979T), Alistipes dispar sp. nov. (5CPEGH6T=JCM 32848T=DSM 108978T) and Alistipes onderdonkii subsp. vulgaris subsp. nov. (3BBH6T=JCM 32839T=DSM 108977T), are proposed.