AbstractThere are a lot of traditional wooden houses, temples and shrines in Japan. These traditional wooden structures have already been standing for a long time. Many of these structural members and joints have suffered from biodeteriorations induced by fungi, termites and so on. It is difficult to know the residual strength of decayed structural members and joints. Therefore it is very important to evaluate the residual strength of structural members and joints for house in use for long term safety, and decide when repair and replacement of the members should be undertaken. The objective of this study is to evaluate the shear strength of nail joints attacked by fungi, which are often used in the wooden houses. In this study, we prepared the partial decayed specimens embedded by nails, and evaluated the shear strength. Those specimens were locally attacked by brown rot fungi (Fomitopsis palustris) for 7 weeks and evaluated the shear strength. In the case of steel nail joint, the shear strength of the decayed wood was higher than those of the sound wood. On the other hand, the shear strength of stainless steel nail joint was slightly decreased by the fungus attack.