Based on the survey examples, there are four patterns of deterioration that tend to occur in plywood bearing walls of wooden houses in Japan. The first is a pattern in which wall is in a whole deterioration. It is a no damage wall or test specimen. The second is a pattern in which only the sill is deteriorating. It is caused by moisture or termites from ground to the base. In addition, there is a pattern in which only one side column of the wall is deteriorated. It is a state in which the straps for downpipe come off and moisture penetrates column from there, causing deterioration. Finally, the upper half of the wall is deteriorated. It represents a state in which water seeps into the upper part of the lower floor from the window or wet area of the upper floor, or a state in which water is flooded due to a leak on the top floor. The shear resistance of the nailed joint with rusted nail and decayed wood is formulated based on the study of the past. And the structural characteristic of the plywood bearing wall in those cases according to the degree of deterioration of the nail and wood is estimated using the results. As a result, it is revealed that the maximum strength doesn’t decrease remarkably when only the sill of plywood bearing wall deteriorates. On the other hand, when the column deteriorates, the rigidity after yield is remarkably reduced. In addition, even if the wood decay a little, the strength increases due to the influence of rusting of the nail, and it decreases when further deterioration progresses.

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