Partner diversity is a key influencer in interorganizational alliances, and several empirical studies have shown that its outcomes are contingent on alliance-specific factors. We extend this research as well as the growing literature on green alliances, in which partner diversity is uniquely high. Specifically, we examine partner-diversity effects on alliance termination in the early stage of green alliance formation. We hypothesize that in this context, size disparity increases termination likelihood, whereas organizational variety and cultural separation have the opposite effect. To test our hypotheses, we use a sample of 366 alliance projects located in Latin America and submitted to the Kyoto Protocol's Clean Development Mechanism for evaluation, validation, and registration from 2004 to 2014. Our findings contribute to several research streams and provide practical guidance for successful formation of alliances focused on environmental protection.