The dry weight and decomp sition rate of dead organic matter in deciduous broadleaved forests were measured at Sanbe Forest of Shimane University. The dry weight of dead organic matter was 4.1-16.8% of above ground biomass in forest ecosystem. Standing dead tree was broken down from the top with decomposition of organic matter, and decreased the total height and specific gravity. Dead trees by girdling also decreased the total hight and specific gravity with the increase of years. However, the trends differed among tree species. The height of standing dead trees did not decrease for 3-4 years after the death of tree, and the decline of the height and specific gravity occurred from five to eight years after.