A Gram-stain-negative, facultatively anaerobic bacterium, designated B6T, was isolated from activated sludge of a wastewater treatment plant in South Korea. Cells were oxidase- and catalase-positive and non-motile rods producing yellow carotenoid-type pigments. Growth of B6T was observed at 20-40 °C (optimum, 37 °C) and pH 6.6-8.2 (optimum, pH 7.0) and in R2A broth supplemented with 0-1 % (w/v) NaCl (optimum, 0 %). B6T contained iso-C15 : 0 as the major fatty acid. Menaquinone-6 was detected as the sole respiratory quinone. The G+C content of the genomic DNA of B6T was 31.5 mol%. The results of phylogenetic analysis based on 16S rRNA gene sequences indicated that B6T formed a tight phylogenetic lineage with members of the genus Cloacibacterium. B6T was most closely related to Cloacibacterium rupense R2A-16T (99.0 %), Cloacibacterium normanense NRS1T (98.7 %) and Cloacibacterium haliotis WB5T (97.4 %), but their DNA-DNA relatedness levels were less than 42.0 %. On the basis of phenotypic, chemotaxonomic and molecular properties, it is clear that B6T represents a novel species of the genus Cloacibacterium, for which the name Cloacibacterium caeni sp. nov. is proposed. The type strain is B6T (=KACC 18988T=JCM 31714T).