The Euripus Strait (Greek: Εύριπος, pronounced [ˈevripos]), is a narrow channel of water separating the Greek island of Euboea in the Aegean Sea from Boeotia in mainland Greece. The strait's principal port is Chalcis on Euboea, located at the strait's narrowest point.

The strait is subject to strong tidal currents which reverse direction approximately four times a day. Tidal flows are very weak in the Eastern Mediterranean, and the strait is a remarkable exception. Water flow peaks at about 12 km/hour, either northwards or southwards, and lesser vessels are often incapable of sailing against it. When nearing flow reversal, sailing is even more precarious because of vortex formation.

The Swiss scholar Francois-Alphonse Forel helped to solve this enigma owing to his study of limnology and the discovery of the seiche phenomenon. But the complete solving of the problem is due to the Greek D. Eginitis, director of the Athens Observatory, who published his conclusions in 1929.

There are two road bridges across the strait, both at Chalcis. One is a two-pylon, cable-suspended bridge built south of town in 1992, and commonly called the "New" or "High" bridge, with a span of about 215 m (705 ft). The strait is 160 m (525 ft) wide at this point. The bridge is accessible via a fork on the main road at Aulis.