A taxonomic study was made of the genus Leuconostoc. The species in the genus were divided into three subclusters by phylogenetic analysis based on the 16S rRNA gene sequences. The three subclusters were the Leuconostoc mesenteroides subcluster (comprising L. carnosum, L. citreum, L. gasicomitatum, L. gelidum, L. inhae, L. kimchii, L. lactis, L. mesenteroides and L. pseudomesenteroides), the L. fructosum subcluster (L. durionis, L. ficulneum, L. fructosum and L. pseudoficulneum) and the L. fallax subcluster (L. fallax). Phylogenetic trees based on the sequences of the 16S-23S rRNA gene intergenic spacer region, the rpoC gene or the recA gene indicated a good correlation with the phylogenetic tree based on 16S rRNA gene sequences. The species in the L. fructosum subcluster were morphologically distinguishable from the species in the L. mesenteroides subcluster and L. fallax as species in the L. fructosum subcluster had rod-shaped cells. In addition, the four species in the L. fructosum subcluster needed an electron acceptor for the dissimilation of d-glucose and produced acetic acid from d-glucose rather than ethanol. On the basis of evidence presented in this study, it is proposed that the four species in the L. fructosum subcluster, Leuconostoc durionis, Leuconostoc ficulneum, Leuconostoc fructosum and Leuconostoc pseudoficulneum, should be transferred to a novel genus, Fructobacillus gen. nov., as Fructobacillus durionis comb. nov. (type strain D-24(T)=LMG 22556(T)=CCUG 49949(T)), Fructobacillus ficulneus comb. nov. (type strain FS-1(T)=DSM 13613(T)=JCM 12225(T)), Fructobacillus fructosus comb. nov. (type strain IFO 3516(T)=DSM 20349(T)=JCM 1119(T)=NRIC 1058(T)) and Fructobacillus pseudoficulneus comb. nov. (type strain LC-51(T)=DSM 15468(T)=CECT 5759(T)). The type species of the genus Fructobacillus is Fructobacillus fructosus gen. nov., comb. nov.. No significant physiological and biochemical differences were found between the species in the L. mesenteroides subcluster and L. fallax in the present study and thus L. fallax remains as a member of the genus Leuconostoc.