Medzhybizh Castle (Ukrainian: Меджибі́зький замок, Medzhybiz'kyi zamok),built as a bulwark against Ottoman expansion in the 1540s, became one of the strongest fortresses of the Crown of the Kingdom of Poland in Podolia. It is situated at the confluence of the Southern Bug and Buzhenka rivers, in the town of Medzhybizh (Polish: Międzybuż), Ukraine. Today the castle is part of the State Historical-Cultural Preserve.
Originally the wooden castle was founded sometime in 1146 by Bolokh (or Bolekhiv) princes. The castle survived the Mongol's invastion, but in 1254 it was dismantled by Daniel of Galicia on the Mongol's orders as several other castles and fortresses in the Kingdom of Rus. The castle was rebuilt by Koriatovych princes after the Grand Duke of Lithuania defeated the Golden Horde at the Battle of Blue Waters in 1362.
Its royal status the castle received already back in 1385, but in 1432 Medzhybizh with most of Podilia was passed to the Polish Crown. The castle was in a state possession for sometime. Sometimes in 1540 the castle was passed to Mikołaj Sieniawski who made some major renovations. The castle's founder was Mikołaj Sieniawski, and the Sieniawski family owned Medzhybizh (Polish: Międzybuż) until its extinction in the early 18th century. The stronghold was reconquered from the Turks in 1699 and passed to the Czartoryski family in 1731.
The last rebuilding effort was undertaken by the Russian imperial authorities in the 19th century. Much restoration has been carried out on the fortress since 1968. Within the walls are a small-scale museum and a church from 1586.