THERE are four submarine hydrothermal activity areas in the Middle Okinawa Trough. They are Izena hole(127°05’E, 27°16’N), Iheya Deep (126°58’E, 27°33’N). Natsushima 84-1 Mound (127°08.6’E, 27°34.4’N), Western mount of Tokunoshima island (127°39’E, 37°52’N), respectively. In an attemptto determine the influence of the Middle Okinawa Trough area hydrothermal activity on copper distributionin the surrounding sediments, 8 surface samples and 6 core samples collected from this area were analyzedfor sequential extraction procedure and bulk analyses. 1 Samples and method Sediment samples were collected at 8 stations by dredger or piston corer (table 1). The sampleswere stored at<4℃, dried at<110℃, and finely ground to pass 200 meshes in an agate mortar.Sequential leaching procedures developed by Tessler were modified as follows: Cu (1) was ex- THERE are four submarine hydrothermal activity areas in the Middle Okinawa Trough. They are Izena hole (127 ° 05’E, 27 ° 16’N), Iheya Deep (126 ° 58’E, 27 ° 33’N). Natsushima 84- 1 Mound (127 ° 08.6’E, 27 ° 34.4’N), Western mount of Tokunoshima island (127 ° 39’E, 37 ° 52’N), respectively. In an attempt to determine the influence of the Middle Okinawa Trough area hydrothermal activity on copper distributionin the surrounding sediments, 8 surface samples and 6 core samples collected from this area were analyzed for sequential extraction procedure and bulk analyzes. 1 Samples and method Sediment samples were collected at 8 stations by dredger or piston corer (table 1). The Sampleswere stored at <4 ° C, dried at <110 ° C, and finely ground to pass 200 meshes in an agate mortar. Sequential leaching procedures developed by Tessler were modified as follows: Cu (1) was ex-