Zvečaj (pronounced [zʋeːt͡ʃaj]) is a medieval ruined castle located on the left bank of the Mrežnica river in modern Karlovac county, Croatia.

Upon the death of Ivan Zvečaj, the castle and surrounding lands were given to Nikola Frankopan Ozaljski by king Matthias Corvinus.

In 1558, the castle was pillaged together with the rest of the possessions of Stjepan Ozaljski, yet it had already been abandoned as a result of the Ottoman wars.

In December 1598, a Turkish army 5000 strong hid in ambush near Zvečaj, Juraj Lenković heard about the force, but underestimated its size.

In 1670, after Fran Krsto Frankopan was imprisoned as a result of the Magnate conspiracy, the castle was looted by the army of Karlovac.