A Gram-negative, non-motile bacterium, designated MJ17(T), was isolated from sludge at the Daejeon sewage disposal plant in South Korea. Comparative 16S rRNA gene sequence analysis showed that strain MJ17(T) belonged to the genus Paracoccus in the family Rhodobacteraceae of the class Alphaproteobacteria. 16S rRNA gene sequence similarities between strain MJ17(T) and type strains of species of the genus Paracoccus were 94.1-97.4 %. The highest similarities were between strain MJ17(T) and Paracoccus homiensis DD-R11(T), Paracoccus zeaxanthinifaciens ATCC 21588(T) and Paracoccus alcaliphilus JCM 7364(T) (97.4, 97.2 and 96.3 %, respectively). Strain MJ17(T) exhibited <22 % DNA-DNA relatedness with P. homiensis KACC 11518(T) and P. zeaxanthinifaciens JCM 21774(T). The G+C content of the genomic DNA was 58.7 mol%. Strain MJ17(T) contained ubiquinone Q-10. The major fatty acids were C(18 : 0) (11.3 %), C(16 : 0) (10.2 %) and summed feature 7 (containing one or more of C(18 : 1)�s7c, C(18 : 1)�s9c and C(18 : 1)�s12t; 54.3 %). Poly-�]-hydroxybutyrate granules are formed. On the basis of phenotypic and genotypic properties and phylogenetic distinctiveness, strain MJ17(T) should be classified in a novel species of the genus Paracoccus, for which the name Paracoccus caeni sp. nov. is proposed. The type strain is MJ17(T) (= KCTC 22480(T) = JCM 16385(T) = KEMB 9004-001(T)).