This work is one of the studies made by the authors on wood properties of forest fertilized Sugi(Cryptomeria japonica D. Don). In this paper, the mechnical properties of fertilized trees and those of non-fertilized ones are compared and studied. The sample trees, which were the same ones as we reported before, were produced in the experimental forest of Kyoto University(Shirahama, Wakayama Prefecture), and in Okutsu-cho, Tomada, Okayama Prefecture. The test pieces are sampled from each tree(at 1. 2-2. 0 m height). Considering the application of wood to wooden columns and beams in the case of constructions, the strength determinations are studied on two types; one is bending and the other compression. The test of compression is carried out on short wooden columns. Moreover, in the compression determination, the samples are tested in three directions: (a)Parallel-to-grain. (b)Perpendicular-to- annual ring. (c)Tangential-to-annual ring. The results may be summerized as follows: (1)The compression of parallel-to-grain and bending strength of fertilized trees are weaker than those of non-fertilized ones. In view of the fact that the strength depends on the width of annual rings and the ratio of late wood, the above result may be understood. However, the compression and bending strength of some fertilized trees in which many false rings are found in the part of late wood, are not always weak. It is considered that the strength depends on the number of false ring cells. (2)The significant difference between fertilized trees and non-fertilized ones is recognized at the 5 % level in the compression of perpendicular and tangential-to-annual ring. But in the tangetial direction to annual rings, the compression strength of non-fertilized trees is weaker than that of the fertilized trees. (3)In the bending modulus of elasticity, it is rather hard to recognized the significant difference between fertilized trees and non-fertilized ones. The mechnical properties of cell in false rings which are found in the part of late wood in fertilized trees seem to play an important part in this bending modulus of elasticity.