1, This investigation was made on the fungi flora of the 21 different forest soils in order to make clear the composition of them. 2. The plots of sampling are the forests of Pinus densiflora S. et Z., Larix Kaempferi Sarg., Thu jopsis dolabrata S. et Z., Fagus crenata Blume, , Crytomeria japonica D. Don., Tsuga canadenis, Carr., Zelkowa serrata Makino., Castanea crenata S. et Z. and peat. 3, As this study was carried out in the course of the forest-soil survey, and 2 to 4 weeks were passed before determining the numbers of fungi in the soil, the no. of fungi determined by the plate method do not show the real no, of the plots. In this investigation therefore, we must be content to know only the relative abundance of the domina nt soil fungi in each sample. The results of experiments are as follows: a. The most common fungi in forest soils are the Genera Penicillium, Trichoderma and Mucor. b. Penicillium and Trichoderma, as might be ekpected, ar the typical groups of soil fungi examined. They were always dominant in all soil samples, occupying generally 20 to 40%, sometimes over 50% of the total no. of colonis. It seems worthy to note that theyy are always as. abundant in the samples taken from lower layers as in those of upper layers. c. Trichoderma are found in dry and wet acid soils, e. g. wind blown or peaty soils, and in the samples taken from those soils the fungi flora are almost all composed of Trichoderma and Penicillium. d. Mucor is also the common genus found in forest soils, but its occurrence also seems to be influenced by soil characteristics. It is relatively abundant in fertile and moderately moistend forest soils, as those of Sugi (C. japonica D. Don.) forests. In the samples of those soils 10 to 25% of the total no. of colonies were Mucor and in the samples of infertile dry and wet acid soils e. g. those of T, dolabrata S. et Z. forest, peaty soils, or wind blown soils, the colonies of this fungus are very few or do not be found. e. It is a marked contrast to the Penicillium and Trichoderma that the no. of colon ies of Mucor of the samples taken from lower layers are very few as compared with those of upper layers. f. Although in some forest soils other Fungi Imperfecti are relatively abundant occu pying 10 to 20% of the total colonies, they are not so important as Penicillium, Trichoderma and Mucor. g. The genera Aspergillius, Rhyzopus and the others ere found only in a few samples and they seem not to be the dominant genera of the fungi flora of forest soils. 4, Classifications of the isolated strains are now under investigation.