Marinomonas posidonica IVIA-Po-181(T) Lucas-Elio et al. 2011 belongs to the family Oceanospirillaceae within the phylum Proteobacteria. Different species of the genus Marinomonas can be readily isolated from the seagrass Posidonia oceanica. M. posidonica is among the most abundant species of the genus detected in the cultured microbiota of P. oceanica, suggesting a close relationship with this plant, which has a great ecological value in the Mediterranean Sea, covering an estimated surface of 38,000 Km(2). Here we describe the genomic features of M. posidonica. The 3,899,940 bp long genome harbors 3,544 protein-coding genes and 107 RNA genes and is a part of the GenomicEncyclopedia ofBacteriaandArchaea project.