In order to improve decaying properties of the plywood the effectiveness of the Malenit treatment on the shear strength and decaying properties of the plywood has been investigated. The results are as follows. 1. No decrease of the shear strength of the plywood has shown despite of whether plywood treated with malenit right after plywood made or veneer treated with the same preservative prior to plywood manufactured. 2. The effectiveness of Malenit treatment on decaying property of the plywood has shown much greater than that of the untreated plywood and red pine sapwood. 3. Weight decreases of the test specimens due to the infection of the different fungi have seen in different ways. If fungi infected are all different in kinds, weight decreases of the specimens are different in it`s degree due to the fungi.