Two strains of gram-negative, catalase- and oxidase-positive, coccus-shaped bacteria, designated NB88(T) and LNB004, were isolated from activated sludge in the Mae-san sewage treatment plant in South Korea. They were characterized in a polyphasic taxonomic study based on phenotypic, phylogenetic and genotypic approaches. Comparative 16S rRNA gene sequence analysis indicated that strains NB88(T) and LNB004 represented a novel subline within the genus Paracoccus in the family Rhodobacteraceae. According to 16S rRNA gene sequence comparisons, strains NB88(T) and LNB004 were indistinguishable and showed 94.5-97.6 % similarity to the type strains of other Paracoccus species. Strain NB88(T) exhibited relatively high levels of DNA hybridization (84±3.5 %) with LNB004 and low hybridization values (<40 %) with type strains of other Paracoccus species. Both strains showed chemotaxonomic characteristics typical of the genus Paracoccus, with Q-10 as the predominant respiratory quinone and C18 : 1ω7c as the major fatty acid, and both strains accumulated poly-β-hydroxybutyrate granules. The DNA G+C contents of strains NB88(T) and LNB004 were 66.4 and 65.1 mol%, respectively. The polar lipid profiles of strains NB88(T) and LNB004 included major amounts of phosphatidylglycerol, phosphatidylcholine and an unknown aminolipid. The taxonomic position of strains NB88(T) and LNB004 was clarified by the low level of DNA-DNA hybridization with closely related strains and the strains could be distinguished from other recognized species by using biochemical tests and molecular genetic analysis. On the basis of their phenotypic and genotypic properties and their phylogenetic distinctiveness, strains NB88(T) and LNB004 should be classified in a novel species of the genus Paracoccus, for which the name Paracoccus limosus sp. nov. is proposed. The type strain is NB88(T) ( = KEMC 5401-184(T) = JCM 17370(T)); strain LNB004 ( = KEMC 5401-001) is a reference strain.