Many studies have tried to explain the inter-firm relationship especially inter-firm cooperation. However, among them, the role of social influence has gotten little empirical investigation or to be neglected. Using survey data from SME tourism enterprises in Vietnam, the study tries to explain inter-firm behaviours based on integrating theories from different disciplines. The study reveals that cooperative intention is the main predictor of cooperative decision. Further, it confirms the positive influence of social impact and similarities between partners on inter-firm cooperation. The study provides theoretical and managerial foundations because the research addresses the relationships among these constructs in inter-firm context.