Leaf biomass of a particular tree species is relatively constant if forest canopy is closed.  Leaf biomass per unit of stem basal area at the lowest crown is proportional to the leaf biomass. From these findings we would expect linkage between basal area at the lowest crown and leaf biomass per unit of basal area.  This study investigated changes of leaf properties in Japanese cedar plantations in four areas by using the data in Ando et al (1968).  Stem basal area at the lowest crown was determined by an equation using tree height, height at the lowest crown and diameter at the breast height.  Stem basal area at the lowest crown increased with increasing forest age but was not different between areas.  Leaf biomass per unit of basal area was not related with forest age but was different between areas.  The results of multiple regression analysis indicated that leaf biomass per unit of basal area was lower where the basal area at the lowest branch was larger and relative yield index (Ry) was lower.  The results suggest that Japanese cedar trees adjust leaf biomass per unit of basal area as affected by forest age and competition between individuals.