The East Sea (the East Sea hereafter) is a semi-enclosed deep marginal sea in the northwestern Pacific. The East Sea is connected with the East China Sea through the Korea Strait, with the North Pacific through the Tsugaru Strait, and withthe Sea of Okhotsk through the Soya and Tartarskiy Straits. As these straits are shallower than 130 m, water exchanges with adjacent seas are very limited. The general upper circulation of the East Sea consists of the cyclonic cold water circulation in the northern part, and north or northeastward flowing Tsushima Current Water circulation south of the polar front. Knowledge of ocean environmental changes is very important because it is closely related with various kinds of other fields including management of resources, stable supply of energy, national defense, and foreign policy. Marine environment has been changed in the East Sea during recent several decades. This ongoing changes include an increase in deep water temperature, decrease of dissolved oxygen in deep water, change of species in fishery, and progress of whitening around the Ulleungdo. Some physical properties such as temperature, wave height at the surface layer of East Sea of Korea were analysed to reveal long-term changes. This paper suggested the necessity of cooperative research with neighboring nations for the fisheries resources management considering the holistic ecosystem concept.he Sea of Okhotsk through the Soya and Tartarskiy Straits. As these straits are shallower than 130 m, water exchanges with adjacent seas are very limited. The general upper circulation of the East Sea consists of the cyclonic cold water circulation in the northern part, and north or northeastward flowing Tsushima Current Water circulation south of the polar front. Knowledge of ocean environmental changes is very important because it is closely related with various kinds of other fields including management of resources, stable supply of energy, national defense, and foreign policy. Marine environment has been changed in the East Sea during recent several decades. This ongoing changes include an increase in deep water temperature, decrease of dissolved oxygen in deep water, change of species in fishery, and progress of whitening around the Ulleungdo. Some physical properties such as temperature, wave height at the surface layer of East Sea of Korea were analysed to reveal long-term changes. This paper suggested the necessity of cooperative research with neighboring nations for the fisheries resources management considering the holistic ecosystem concept.