Pollen analysis of deposits from Ochiishi Mire was made with special references to the vegetation history of Nemuro Peninsula in easternmost Hokkaido since the Late Pleistocene. A landscape consisting of grassland and birch forest was seen around this area ca. 11500 years ago. Thereafter, conifers such as spruce, fir and larch began to invade and formed boreal forests. These coniferous forests, excluding larch, continuously occupied this area until ca. 6000 years ago. Though the coniferous forests deteriorated due to climatic warming, cool temperate deciduous forest has not fully developed in this area yet. The cool temperate oak forest slightly decreased and boreal birch forest developed in the peninsula ca. 2500 years ago.