Rudkhan Castle (Persian: قلعه رودخان; Gilaki: رودخان دژ), also Roodkhan Castle, is a brick and stone medieval fortress in Iran that was built to defend against the Arab invaders during the Muslim conquest of Persia. With the fall of the Sasanian Empire, this area became a defensive position against the Arabs in the then-newly established Tabarestan.

Located 25 km southwest of Fuman city north of Iran in Gilan province, it is a military complex which was constructed during the Sasanian era (224-651), and later rebuilt in 1096 by the Nizari Isma'ilis for use by the Assassins. The castle is built on two tips of a mount, with an area of 2.6 hectares (6.4 acres).

The Rudkhan Castle River originates in the surrounding heights and flows from south to north. Rudkhan Castle sits at the two peaks of a mountain at elevations of 715 and 670 metres and contains strong fortifications and battlements at a length of 1,550 metres.