The social norm-based intervention is a frequently used tool for encouraging pro-environmental behavior. In designing effective interventions, however, both practitioners and researchers need more knowledge about the relationships between different norm constructs and pro-environmental behavior. In this study, we meta-analyze the predictive strength of injunctive, descriptive, and personal norms using meta-analytical structural equation modeling (MASEM). Data are extracted from 572 studies reported in 534 articles across 56 countries with a total sample size of N = 312,127. We find that internalized (i.e., personal) norms are consistently the strongest predictor of pro-environmental behavior and that personal norms mediate most of the impacts of injunctive and descriptive norms. Both injunctive and descriptive norms predict pro-environmental behavior, uniquely and with similar strengths. We find no significant moderations of collectivism or behavioral cost on the predictive strength of social norms on pro-environmental behavior.