Okushiri Island is located on the Okushiri Rise, which is regarded to be an active zone adjacent to the nascent trench as the plate bonudary between the Eurasian and North American plates (e. g. Nakamura, 1983), continuing from Japan Basin to Toyama Trough (Fig. 1). This island is composed of a series of Pleistocene marine terraces up to the top of the island, 584m high. The height of the last interglacial terrace ranges from ca. 120m to the north to ca. 70m to the south, showing a southward downtilting with a slight easterly component. The maximum uplift rate since the last interglacial age is estimated at 0.9m/1, 000 yrs (Miyaura, 1975). Holocene marine terraces are observed intermittently along the east coast and are subdivided into two, the upper and the lower, at some places (Figs. 2 and 3) . The width of terraces is less than about 50 m except the northern and southern tip of the island. Terrace deposits, composed of coarse sand and rounded gravel without fine matrix, are less than 1 m in thickness, indicating a mainly wave-cut origin for these terraces (Fig. 4) . A glassy tephra layer of about 10 cm thick overlies on a buried soil developed on the lower terrace deposits, or interbedded within dune sand, formed on the upper terrace. This tephra probably erupted about 500 y. B. P., judging from 14C date of the buried soil, immediately beneath the tephra layer, and is tentatively named “Ok tephra”. The height of marine limit or of the inner edge of terraces is about 8_??_40m a, m. s.1. for the upper terrace and 4_??_6m a. m. s. 1, for the lower one. The presence of the late, Jomon archeological site on the upper terrace at Yamasetomari indicates that the upper terrace has emerged ca. 4, 000 y. B. P. at the latest and is probably correlated with the Holocene terrace of the other parts of Hokkaido, which was formed in association with the postglacial sea level rise, the culmination of which was ca. 6, 000 y. B. P. The lower one is assumed to have emerged considerably earlier than ca. 500 y. B. P., based on the age of buried soil underlying Ok tephra. An exact age of the emergence of these terraces, however, is not confirmed. On the other hand, Holocene lowlands are developed near the mouth of the Aka River and Wasabiyachi River at an altitude of 6_??_8m a. m. s. 1. and are traced inland along the rivers (Fig. 5). Excavations were carried out at four localities on these lowlands in order to collect continuous samples for the facies observation, radiocarbon dating and diatom analysis. The lowland is underlain by a terrestrial peat layer up to 3 m in thickness overlying a marine silt and sand bed, whose upper limit, identified by the facies and diatom analysis, is about 4m a. m. s. 1. near the river and about 6m amsl near the valley edge (Figs. 6 and 7). The 14C date from the upper part of the marine bed is ca. 4, 600 y. B. P. and that obtained from the basal part of the peat bed is ca. 4, 000 y. B. P. Accordingly, the emergence of these lowlands is assumed to have taken place nearly at the same time, when the upper terrace along the coast emerged. The above-mentioned marine bed possibly represents the latest phase of the postglacial transgression and its emergence may be later than that of the open coast in such a lowland along the river. It is certain that at least two relative sea level stillstands during the Holocene are recorded in Okushiri Island. The rate of uplift since the formation of the upper terrace is estimated to be at least 1.2m/1, 000 yrs under the assumption that the sea level of ca. 6, 000 y. B. P. was 2m higher than the present one. It is equal or slightly higher than that for the last interglacial terrace. In Hokkaido, such a high rate of uplift can be found only in Okushiri Island and the western coast, as far as our investigation proves (Fig. 8).