This paper dealt with the composition of species, the relation between D_0 and H, and biomass of understory in a deciduous broad-leaved forest.
1. The number of tree species which appeared in sampling plots attained to fifty species. The species which the frequency were rather high were as follow, Lindera umbellata, Lonicera gracilipes, Viburnum erosum, Viburnum Wrightii, Callicarpa japonica, Callicarpa mollis, Ligustrum obtusifolium, Euonymus oxyphyllus, Pouthiaea villosa var. laevis, Car pinus laxiflora, Styrax Obassia and Clethra barbinervis.
2. The number of small understory(H＜100cm) increased with the increase of total number of understory. But the number of big understory became constat. The number of understory depended on the relative light intensity in forest floor.
3. The relation between D_0 and H of understory was expressed as the following equation, 1/H=A/D_0+B. The parameter of A and B differed by tree species.
4. The above ground biomass of understory were able to estimate by logarithmic regression on ΣD^2_0･H without using the clipping method.