Opuzen [ ɔpuzɛn ] (it. Forte Opus ) is a small town in Croatia. The town on the left bank of the Neretva River, 12 km upstream from its mouth in the Adriatic Sea, part of the Dalmatian Dubrovnik-Neretva county. Opuzen has 3,254 inhabitants ( 2011 census ).

In the Middle Ages the town was named Posrednica. In the 14th century it is a market town and is part of the Dubrovnik Republic. End of the 15th century a fortress was built first; the Venetians built on the same spot the Fort Opus, whose name bears the town today.