The oceanographic observations in the Okhotsk Sea were made on board the patrol ship “Soya” in the prevailing period of drift ice in 1964, 1965 and 1966. The older data obtained by the Hydrographic Office of Japan from 1935 to 1940 were also examined.It was ascertained that the Open Water, that is ice-free area always existed in the southern part of the Okhotsk Sea. This open water is maintained ice-free by the inflow of warm water from the Pacific Ocean through the straits between the Kurile Islands.The movement of water flowing in and out between the islands was investigated and the amount of water transport was estimated.The results are as follows:1) There exists throughout the year the West Kamchatka Current, (a tentative name), which flows northwards into the Okhotsk Sea between the Kurile Islands. In winter season, this current suppresses drift ice which flows down to south, and makes ice-free open water area. The area of this open water is about 0.2-0.5 × 106 km2, which is one fifth of the total area of the Okhotsk Sea.2) The main ocean current system in the Okhotsk Sea is composed of the West Kamchatka Current which flows toward north along the west coast of the Kamchatka Peninsula and the East Sakhalin Current which flows toward south off the east coast of the Sakhalin, and several counter currents and vortices between them.3) The water flux of 15.0 × 106 m3/sec, on the average, flow in and out between the Kurile Islands from winter to spring.4) Through the North Uruppu Sound, which is the largest channel between the Kurile Islands, the large flux flows out toward south in the upper layer and is estimated to be about 5.0 × 106 m3/sec.