The South Euboean Gulf (, Notios Evvoïkos Kolpos) is a gulf in Central Greece, between the island of Euboea and the Greek mainland. With a total length of approximately 50 km and a width of 10 to 20 km, it stretches nearly diagonally from northwest to southeast, from the Euripus strait, which connects it to the North Euboean Gulf, to the Petalies Gulf near Agia Marina in the south.