A new species of the genus Xouthous Thomson, 1883, previously known as Idomene, obtained from the 1995–2015 collections, from the coasts of the Korean Peninsula, is described and illustrated. To date 16 valid species of the genus including X. yeonghoonisp. nov. presented herein, have been reported from the Antarctic, Atlantic, Indian, and Pacific oceans. The new species can be easily distinguished from its congeners by the combination of the following characters: 7-segmented female antennule; antenna with 2 exopodal segments; mandibular exopod with 2 lateral strong spines and 4 distal plumose setae; exp-3 of P2–P4 with 2 strong pectinate spines; and P5 baseoendopod with truncate margin, and spatulate and parallel-sided setae. In addition to the description of the new species from Korea, comparisons to 5 closely related congeners (“palisade group”) from the Indian Ocean are also included. Finally, a mini-review on the global distribution of the genus, with a taxonomic revisit to X. laticaudatus sensu Kim (2014), is provided. The new species described herein is the first record of Xouthous from East Asia.