Based on the positive youth development (PYD) framework, the protective-protective model, and the conservation of resources theory, this study examined the negative moderating effect of hope between peer trust and six types of prosocial behaviors (emotional, dire, altruistic, compliant, anonymous, and public) among rural left behind adolescents (LBAs) and analyzed the difference of the moderating effect of hope between LBAs and nonLBAs. A total of 700 rural LBAs and 673 rural non-LBAs in Fujian province were surveyed using the Peer Trust Scale, Hope Scale, and Prosocial Tendencies Measure. Correlation analysis showed that peer trust, hope, and six types of prosocial behaviors were all positively correlated. Moderated analysis revealed that peer trust had a stronger influence on emotional, dire, altruistic, and compliant prosocial behavior under a low level of hope in LBAs. Compared with LBAs, hope did not moderate the relationship between peer trust and emotional, dire, and compliant prosocial behavior in non-LBAs. This study revealed the moderating mechanism of LBAs' peer trust and prosocial behavior and might help them to improve their prosocial behavior.