In February to March, 2004, 17 specimens of sail-fin sandfish, Arctoscopus japonicus, were collected off the Iwate area, Pacific coast of northern Honshu, Japan, during research on fishery resources by Iwate Fisheries Technology Center. Using all the specimens, a sequencing analysis of the mitochondrial control region was performed, and we found that they have a genetic composition closely approximating to the western Japan population distributed north of Oki Islands, the Sea of Japan. These specimens were estimated to be three years old, belonging the 2001 year-class. This year-class from the Akita coast area became a very large resource, and this may have led to the expansion of their distribution. The occurrence of sandfish off the Iwate area in 2004, should be an event through the enlargement of distribution area of the 2001 year-class that hatched along the Akita coast area.