Often in Japan, conversion of forest type has not yielded productive plantations, but the composition of that stand has not been analyzed. This paper discusses the growing structure and the management of the unproductive stand of Sugi (Cryptomeria japonica) plantation at Akasai National Forest located in the middle part of Hyogo Prefecture, investigated in Novenber, 1988. This stand was cultivated by ordinary weeding and improvement cutting since the Sugi seedlings were planted at about 3, 000 per hectare for about 82 hectares 30 years ago, after the natural forest of broad leaved tree mixed a few with natural Sugi was clear cut. In the research stand on the lower-slope, the forest crown closes and forms a monostratum of planted Sugi. As the mean height of dominant tree is about 13.2 m, the stem growth tends to be nearly equal in mean value of general Sugi plantation. On the contrary, the planted trees at the upper research stand are mostly alive, but there are numerous oppressed trees growing poorly such as those with bended stem base or slant stem by snow pressure. The dominant tree is about 30% of the total number and establishes aggregately, and this mean height is about 6.8 m as half that of the lower research stand. In addition, the Sugi poor plantation is mixed in the whole stratum with broad leaved tree naturally regenerated after close of weeding, and the number of the tree over 3 m in height so far is about 10, 000 (Table 1, Fig. 1, 2 ). The distribution of the tree height and the diameter at breast height of Sugi in the upper research stand resembles that of the L type, and the existing stand forms a multistoried structure which is continuous in stratification. On the other hand, that distribution of lower research stand tends to indicate a nearly normal distribution (Fig. 3, 4 ). The distribution of broad leaved tree also resembles that of L type, and the ratio of the useful broad leaved tree as higher height class is larger than the small (Fig. 5 ). Judging from the process of diameter and height growth by the stem analysis of sample trees (Fig. 8, 9 ), the growth of Sugi at the lower research stand is recognized to be vigorous without interruption, but the growth of most of Sugi at the upper research stand is continuously small after planting. It seems that the poor growth of the upper research stand is caused by sterile soil such as shallow soil layer and abundant gravel (Table 2). Therefore, this poor plantation by the conversion of forest type can be said to be a failure stand of afforestation to come from a mistake of judgment for the fitting site of planting. However, as the Sugi dominant tree or the useful broad leaved tree in the upper plantation grows depending on the soil environment, the multi-storied forest of few mixed artificial Sugi and natural broad leaved tree may be formed if the existing stand is succeeded on the natural status. Furthermore, the improvement cutting by adequate control of the number of some broad leaved trees excluding useful trees may .be an effective means of forest management.