Abstract: Key suppliers’ participation in complex product innovation is beneficial to the final success. However, it may also induce opportunistic behavior for rent appropriation, due to the existence of specific asset investment and intellectual properties. Based on transaction cost theory and relational governance literature, this paper examines the governance role of long-term orientation on key suppliers’ opportunistic behavior, from a bilateral perspective. The key findings based on 205 survey data from complex product integrator enterprises show that: 1) both the explicit and implicit opportunistic behavior will weaken the positive effect of integrator’s technological knowledge integration on its innovation performance; 2) long-term orientation from both the integrator and its key suppliers’ side can weaken the negative moderating role of explicit opportunistic behavior on the above main effect significantly; 3) the effect size of long-term orientation’s governance effect varies depending on who is the behavior and what kind of opportunistic behavior it is. This study emphasizes on the investigation of the multi agents’ interactive behavior in micro level during cooperative innovation. Besides, it contributes to the practice by indicating the integrator to governance in prevention, that is, to select key suppliers who have the willingness to cooperate in the long run, since the first beginning of the relationship.