A novel Gram-positive, aerobic bacterium, strain JH1T, was isolated from deep-sea sediment of the East Sea, South Korea, and identified by methods of polyphasic taxonomy. The strain was oxidase-positive, motile and coccus-shaped. The genomic DNA G+C content of strain JH1T was 47 mol%. The major fatty acid of strain JH1T was anteiso-C15:0 and the predominant menaquinones were MK-7 and MK-8. Similarity of the 16S rRNA gene sequence (1452 nt) of strain JH1T to those of species of the genera Planococcus and Planomicrobium was 96.0-98.2%. The signature nucleotides in the 16S rRNA gene sequence were compared with those of previously studied type strains of species in the genera Planococcus and Planomicrobium, and suggested that strain JH1T belongs to the genus Planococcus. In addition, phylogenetic analysis showed that strain JH1T was located within the cluster comprising Planococcus antarcticus and Planococcus kocurii. DNA-DNA hybridization showed that it had 9.3% genomic relatedness with Planococcus antarcticus DSM 14505T and 22.9% with Planococcus kocurii DSM 20747T. On the basis of the phenotypic, phylogenetic and genomic data, a novel species of the genus Planococcus, Planococcus donghaensis sp. nov., is proposed, with type strain JH1T (=KCTC 13050T=LMG 23779T).