A Weibull function was used to model the vertical distribution of leaf area of individual trees in a 25-year-old Chamaecyparis obtusa (Siebold & Zucc.) Endl. plantation. The parameter representing the shape of the leaf distribution was independent of tree size. A scale parameter tended to decrease with tree size suggesting a critical minimum height for retention of foliage by trees. On the basis of leaf distribution, the photosynthetic production of individual trees was estimated from the canopy photosynthetic production, which was determined from a model of canopy photosynthesis. The data indicated that the photosynthesis of a tree was proportional to the corresponding tree weight to the power of 1.84. Furthermore, the photosynthetic production varied as the 3/2nd power of total leaf area of the tree. Thus, it was concluded that the photosynthetic production per unit of leaf area, that is, the mean photosynthetic activity of a tree, is proportional to the stem girth at clear length, or the square root of the leaf area of the tree.