As a critical bridge between societal needs and civic participation, nonprofit transparency is essential to gain trust and support from potential donors. While a considerable number of existing empirical studies have explored the relation between nonprofit transparency and donations, the causal impact and mechanisms of nonprofit transparency on donations are still not answered well. This study employs a 3 (Financial Transparency: High/Medium/Low) × 3 (Performance Transparency: High/Medium/Low) survey experimental design (N=1200) to explore the causal relation and mechanisms between nonprofit transparency and donations, as well as the heterogeneous effects of financial transparency versus performance transparency on donations. Analysis of experimental data reveals that both financial and performance transparency significantly increases willingness to donate and amount of donations, while potential donors are more sensitive to signals of financial transparency than performance transparency. In addition, rationality of donors serves as a positive moderator between transparency and donations, while past donations have a mediated moderation effect through trust in charitable organizations. These novel findings can not only contribute to the literature by further expanding the signaling theory, but also provide empirical evidence and practical implications for policymakers and nonprofit managers to promote nonprofit transparency and accountability.