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In order to clarify the structure and seasonal variability of the flow field near the western boundary of the Sea of Okhotsk, long-term mooring measurements were carried out from 1998 to 2000 in this region. In most of the mooring period a persistent southward flow (the East Sakhalin Current) was observed, which extends from the surface to a depth around 1000 m. The speed of this southward flow clearly changed seasonally. The peak monthly mean speed along 53°N at a depth of 200 m attained a maximum of 37 ± 9 cm s[sup -1] in January and a minimum of 10 ± 8 cm s[sup -1] in July. Three different cores of intense flow were identified in the southward flow. The first core was centered over the continental slope and had rather large vertical extent, reaching the bottom on the slope. The second core was trapped over the shelf near the surface and was observed from October to November. This core was associated with less saline surface water affected by the Amur River discharge. The third core was intensified toward the bottom on the slope. The spatial and temporal distribution of this bottom-intensified core coincided with that of dense shelf water, which is formed over the broad shelf in the north. The intensity of this core damped within a few hundred kilometers from the northern end of Sakhalin probably because of strong mixing of dense shelf water with surrounding waters. The total transport of the southward flow at 53°N was 6.7 × 10[sup 6] m[sup 3] s[sup -1] in the annual average, varying from a maximum of 12.3 × 10[sup 6] m[sup 3] s[sup -1] in February and a minimum of 1.2 × 10[sup 6] m[sup 3] s[sup -1] in October. Most of the transport was maintained by the first core of the southward flow. [ABSTRACT FROM AUTHOR]