The writer have been studied the effect of coverture by forest litter and brush on the improvement of growth in the Hinoki (Chamaecyparis obtusa) plantation which was growing only about 1 meter when 15 years old, and following results obtained. 1) Hinoki trees which was covered the ground by forest litter and brush are showing more than 6 times in growth of volume comparison with non treated area. But these effect continued no more than 3 or 4 years after the coverture settled. 2) The chemical character of soil are improved by the proceeding method. For example, the compornent of all nitrogen and organic matter increased well. 3) This method is effective when we expect more rapid growth in limited years. But if we expect the successive improvement of forest, we must take some mixed plantation with broad-leaved-trees at the same time as the soil improvement by the litter and bruth.