于山国（朝鲜语：우산국）是一个在古代存在的国家，领土包括了郁陵岛和附近岛屿。

《三国史记》说明了于山国在朝鲜三国时代时就已存在。在512年，新罗的将军异斯夫攻打于山国，使于山国向朝鲜本岛臣服。不过，到了11世纪初，于山国受到女真族的海盗侵略而灭亡。

韩国人认为古代名称的于山岛是和日本争执的独岛，但日本人认为于山岛是在郁陵岛接近的竹屿。

李氏朝鲜柳馨远《东国舆地志》(1656),

于山岛 欝陵岛
一云武陵 一云羽陵 二岛在県正东海中 三峰及业掌空 南峰梢卑 风日清明则峰头树木 及山根沙渚 歴々可见 风便则二日可到 一说于山 欝陵 本一岛　地方百里

Usan-guk, or the State of Usan, occupied Ulleung-do and the adjacent islands during the Korean Three Kingdoms period. According to the Samguk Sagi, it was conquered by the Silla general Kim Isabu in 512. He is said to have used wooden lions or tigers to intimidate the residents into surrendering. Usan-guk rarely enters into historical records, but appears to have continued a largely autonomous existence until its annexation to Goryeo in 930.