Abstract: Using the poplar as materials, the authors examined and compared the activity of lipoxygenase (Lox) and the dynamic level of ABA and JA in different leaves: the mechanical damaged leaves and the leaves of the neighboring healthy plant after being damaged. The result showed that: (1) the mechanical wounding enhanced the activity of Lox and induced the concentration of ABA and JA increasing in the leaves. It could be concluded that mechanical wounding could induce the defensive of the damaged plant. Furthermore, there might exist some airborne signals, which transferred the wounding message to neighboring plants, and induced defense reaction of the neighboring healthy plants. (2) Lox activity and the contents of ABA and JA increased with similar trend along with the mechanical wounding, indicating that Lox maybe act to the key process of the biosythesis to ABA and JA.