Vertically homogeneous water was found around the convex coast of Jeju Island on its west side from hydrographic surveys conducted in June and Ictober 1980, and June 1981. This is the first time that this hydrographic structure is observed. Historical data do not show this water, since they wewe taken far from the island. The presence of this homogeneous water is explained in terms of tidal mexing for the lower half of the water column and relling for the upper half of the columa which conserve vorticity as currints flow clockwise around the island. Direct measurement in future is required to prove the upwelling mechanism.