A Gram-stain-positive, strictly aerobic, non-motile, non-spore-forming and oval-shaped bacterium, designated strain BO-16T was isolated from activated sludge. In this study, we describe the taxonomic characterization and classification of this bacterium by using the polyphasic approach. Growth of BO-16T was observed at 10–40 °C (optimum, 25–37 °C) and at pH 5.0–10.0 (optimum, pH 7.0) on R2A agar. The major fatty acids it contained were iso-C16:0, anteiso-C17:0 and iso-C17 : 0 and the major polar lipids were diphosphatidylglycerol, phosphatidylinositol and phosphatidylethanolamine. This isoprenoid quinones included MK-8 (H4) and MK-8 (H6). The peptidoglycan contained lysine, serine, alanine, glycine and glutamic acid and represented the peptidoglycan type A4α. On the basis of 16S rRNA gene sequence similarity, BO-16T was shown to represent a member of the genus Flexivirga and to be related to Flexivirga oryzae KACC 18597T (98.4 % sequence similarity), Flexivirga endophytica KCTC 39536T (97.5 %), Flexivirga alba DSM 24460T (97.4 %) and Flexivirga lutea KCTC 39625T (97.3 %). The G+C content of the genomic DNA was 68.0 mol%. The DNA–DNA relatedness values between BO-16T and its closest phylogenetic neighbours were much lower than 70 %. BO-16T could be differentiated phylogenetically and phenotypically from the species of the genus Flexivirga with validly published names. Therefore the isolate represents a novel species, for which the name Flexivirga caeni sp. nov. is proposed, with the type strain BO-16T (=KACC 19647T=LMG 30859T)