Otočac (pronounced [ɔtɔ̌tʃats]; German: Ottochaz, Latin: Ottocium) is a town in Croatia, former bishopric and present Latin Catholic titular see. It lies in the northwestern part of Lika region, in the Gacka river valley. The population of the town is 4,354 as of 2001, with a total of 10,411 people within the municipality at large, the majority of whom are Croats (91%).
Otočac was named after the early Croatian parish. The text of the famous Baška Tablet (around 1100) says that the church of St. Nicholas in Otočac was part of the order community with the Church of St. Lucy, Jurandvor on the island of Krk.
From 1300 on, it belonged to the estate of the Frankopan family. Sigismund Frankopan (1461–1535) founded a diocese there (see below).
The settlement with a defence tower, at a bend in the river Gacka, was protected by a towered fort. After the fort's demolition in 1829, only parts remained preserved. To provide a safer defence, a Renaissance-era castle ("Fortica") was built in 1619, with a triangular layout of cylindrical towers (these ruins stand above the town).