The purpose of this study is to clarify the effect of compression creases on mechanical properties of woods damaged by typhoon. Sugi (Cryptomeria japonica) trees from seedling and two cartivars (kumotohshi and yabukuguril and hinoki (Chamaecyparis obtuse) trees were examined in this study. The results were summarized as follows; 1) macroscopic compression creases were occured in the stem of seedling sugi and cv. kumotohshi and hinoki, and in many cases comcentrated on one side of the stem. These were distributed up to 2/3 height of the tree from the ground level and marked at 1/4 to 1/3 height (Fig. 2 and Fig. 3). In addition to macroscopic compression creases, microscopic fractures were distributed widely in the tracheid cell walls in the compression crease side of the stem (Fig. 4) 2) White-colored spots were observed on the under side surface of cv. yabukuguri stem bended by typhoon. Trust-lines and slip planes were found in the tracheid cell walls in the under side of the stem (Fig. 5). 3) It was experimentally clear that mechanical properties of small specimens were influenced markedly because of macroscopic compression creases and also affected by microscopic fractures but not as remarkably as macroscopic compression creases (Table 1 and Table 2). 4) In most cases load-deflection or stress-strain curves in the specimens including macroscopic compression creases or microscopic fractures did not show simple line in the range of low load (Fig. 6 and Fig. 7).