To establish the method of efficient cultivation for Polygala tenuifolia, the effect of sowing density on root yield was investigated. The sowing density did not affect on the survival rate. The higher the sowing density, the higher the number of plants and the higher the total fresh weight of root per plot. On the other hand, the sowing density affected the individual plant size. The rate of small root (less than 2 g) was 58.1 % when the density was 5 g seed per plot, but 85.8 % when the density was 50 g seed per plot. For ordinary cultivation, 5.7 kg of seed/ 10 a gave good results, i.e. 178 kg fresh root (76 kg dry root) per 10 a. Furthermore, this density did not require laborious thinning.The sowing density of 1.4-2.8 kg/10 a was the exceptionally recommended density for producing the crude drug "Niku-onji" of good quality (dried cortex of this species).