琉球海沟（日语：琉球海沟（りゅうきゅうかいこう）或称南西诸岛海沟）是太平洋的海沟，位于日本南部和**东北部，海沟沿着日本琉球群岛东南侧的菲律宾海往下伸延，长度2,250公里（1,398英哩），最大深度5,212米（17,100英哩）。

琉球海沟是由菲律宾海板块潜入欧亚大陆板块所形成的板块边界。由于缺乏相关震灾纪录，琉球海沟向来被认为不会发生大地震。然而近年学者研究发现，琉球海沟暗藏菲律宾板块紧黏着欧亚板块的“固着区”，学者判断欧亚板块不但黏着菲律宾海板块，两者之间还有连动作用。

The Ryukyu Trench(琉球海沟,Ryūkyū kaikō), also called Nansei-Shotō Trench, is a 1398 km (868 mi) long oceanic trench located along the southeastern edge of Japan's Ryukyu Islands in the Philippine Sea in the Pacific Ocean, between northeastern ****** and southern Japan. The trench has a maximum depth of 7460 m (24,476 ft). The trench is the result of oceanic crust of the Philippine Plate obliquely subducting beneath the continental crust of the Eurasian Plate at a rate of approximately 52 mm/yr . In conjunction with the adjacent Nankai Trough to the northeast, subduction of the Philippine plate has produced 34 volcanoes. The largest earthquake to have been recorded along the Ryukyu Trench, the 1968 Hyūga-nada earthquake, was magnitude 7.5 and occurred along the northernmost part of the trench on April 1, 1968. This earthquake also produced a tsunami.