Rumoi Subprefecture (留萌振興局, Rumoi-shinkō-kyoku) is a subprefecture of Hokkaido Prefecture, Japan. As of 2011, it had a population of 52,627 and an area of 4,019.97 square kilometres (1,552.12 sq mi). The population density of the subprefecture, 13 people per km², is very low compared to the rest of Japan.