The deep sea, the largest biosphere on Earth, nurtures a large variety of animals. However, no virus that infects deep-sea animals has been found. We herein report the first full-length RNA viral genome sequence identified from the deep-sea animal, Osedax japonicus, called Osedax japonicus RNA virus 1 (OjRV1). This sequence showed the highest amino acid sequence similarity to a virus of the family Togaviridae. However, the phylogenetic position and genome structure of OjRV1 differed from those of viruses in Togaviridae. These results suggest that OjRV1 belongs to a new virus family and that deep-sea animals may associate with new viruses.