A Gram-negative, non-motile, catalase- and oxidase- positive, strictly aerobic, and short rod-shaped bacterium that was designated strain KOPRI 25157(T) was isolated from coastal seawater sample in Antarctica. The temperature and pH ranges for growth on R2A agar were 10-20°C, and 5.0-10.0, respectively. Phylogenetic analyses of the 16S rRNA gene sequence of strain KOPRI 25157(T) showed it to belong to the family Oxalobacteraceae of the class Betaproteobacteria, and it formed a distinct clade from other recognized members of the family. DNA G + C content was 65.9 mol%. Major ubiquinone was Q-8. Predominant cellular fatty acids were C(16:1) ω7c/15 iso 2OH (56.4%) and C(16:1) (30.5%). Major polar lipids were phosphatidylglycerol, phosphatidylethanolamine, and unknown lipid. On the basis of these data, it is proposed that strain KOPRI 25157(T) is the representative of a novel genus, for which the name Actimicrobium gen. nov. is proposed in the family Oxalobacteraceae. The type strain for Actimicrobium antarcticum sp. nov. is KOPRI 25157(T) (=JCM 16673(T)=KCTC 23040(T)).