This study explored how and when positive contact between residents and tourists stimulates tourists’ environmentally responsible behavior. Drawing on social exchange theory, we verified a moderated mediation model in which gratitude mediated the link between positive contact and tourists’ environmentally responsible behavior, while agreeableness moderated the relationship between positive contact and gratitude. Data were collected from 691 visitors to Mount Wuyi. The findings revealed that positive contact directly affected tourists’ environmentally responsible behavior and that this link was mediated by gratitude. Furthermore, agreeableness significantly moderated the effects of positive contact on gratitude. In particular, the effect of positive contact on gratitude was stronger for tourists with high agreeableness. Additionally, agreeableness also strengthened the indirect relationship between positive contact and tourists’ environmentally responsible behavior through gratitude—which was, again, stronger for highly agreeable tourists.