A new pardaliscid amphipod, Princaxelia marianaensis sp. nov., is described from a single female captured at the Shinkai Seep Field, Mariana Trench, from a depth of 5,689–5,683 m. A key to species of Princaxelia is provided. This is the first species of Princaxelia to be described from the Mariana Trench, and the second report of this genus from this region.