Chusansŏng () was a Gaya-era Korean fortress in what is now Goryeong County, North Gyeongsang Province, South Korea. It also went by the name Isansŏng () On January 21, 1963, it was made Historic Site of South Korea No. 61.
It was built on the mountain Jusan. Relics that were characteristic of Gaya culture of the 5th to 6th centuries have been found at the site. It had two sets of walls. The inner walls were in a long oval shape. Both sets are mostly collapsed.