Two Gram-negative, chemoheterotrophic, non-motile strains, Mok-1-36T and MAOS-86T, were isolated from marine-sediment samples collected from the coasts of Okinawa island and the city of Odawara in Japan, respectively. Phylogenetic studies based on 16S rRNA gene sequences indicated that Mok-1-36T and MAOS-86T were members of the family Flavobacteriaceae, clustering with members of the genera Ulvibacter and Vitellibacter, respectively. Strains Mok-1-36T and MAOS-86T shared pairwise 16S rRNA gene sequence similarities of 93.5 and 89.1 % with the type strains of Ulvibacter litoralis and Vitellibacter vladivostokensis, respectively. Phylogenetic distinctiveness and phenotypic differences from their phylogenetic neighbours indicated that these strains represent two novel species and genera within the family Flavobacteriaceae, for which the names Sediminibacter furfurosus gen. nov., sp. nov. (MAOS-86T) and Gilvibacter sediminis gen. nov., sp. nov. (Mok-1-36T) are proposed. The type strain of Sediminibacter furfurosus is MAOS-86T (=NBRC 101622T=CIP 109285T) and the type strain of Gilvibacter sediminis is Mok-1-36T (=NBRC 101626T=CIP 109286T).