The distribution of above ground biomass of understory in a stand and the differences among some stands of which age differed were studied in Sugi(Cryptomeria japonica D. Don) stands in Sanbe Forest of Shimane University. The standing crops of woody plant and Sasa were occupied to total vegetation, 44% and 51%, respectively. The standing crops of understory gathered in the part around the gap of crown, but the amount was not always related to the relative light intensity. The amount of the standing crops of understory decreased with the increase of stand age until stands were close and that increased gradually as the relative light intensity of stands increased again because of thinning and pruning. The amount of the standing crops of understory decreased also as the stem-form coefficient decreased.