The taxonomic position of a marine actinomycete, strain SJS0289/JS1T, was determined using a polyphasic taxonomic approach. The organism, which had phenotypic properties consistent with its classification in the genus Williamsia, formed a distinct clade in the 16S rRNA gene tree together with the type strain of Williamsia muralis, but was readily distinguished from this species using DNA-DNA relatedness and phenotypic data. The genotypic and phenotypic data show that the organism merits recognition as a new species of Williamsia. The name proposed for the new species is Williamsia maris; the type strain is SJS0289/JS1T (=DSM 44693T=JCM 12070T=KCTC 9945T=NCIMB 13945T).