Shizukari Mire is situated along the south-western Pacific coast of Hokkaido. Once it had a beautiful and excellent landscape due to various community types and high species diversity with many ponds and floating-islands. It was designated as a national natural monument in 1922. But this status was cancelled in 1951. Analysis of old topographical maps and documents revealed that, the reason for the cancellation was not the devastation of the mire but the pressure to develop agricultural lands. The size of the mire was 263 ha in 1917. In 1953, two years after the cancellation, it became 221 ha. Then the mire was converted rapidly into agricultural land and by 1996 it was reduced to only 34 ha. The remaining mire is the center part of the former bog and includes some pond vegetation. Two substitutional community types are recorded at the hollow, the Rhynchospora alba - Drosera rotundifolia community and the Rhynchospora fauriei - Rhynchospora alba community. Most of the remaining mire had been covered with lawn vegetation which has changed into substitutional vegetation, the Rhus trichocarpa - Moliniopsis japonica community by drainage and theft. The conservation and rehabilitation of the mire are needed immediately because the succession is continuing and the remaining mire is in very dangerous condition.