This study examines the Kyoto Protocol's impact on the international diffusion of renewable energy technologies including solar and wind energy. Using patent application data of 133 countries from 1990 to 2013 and a difference-in-difference approach, we find that the Kyoto Protocol increased international patent applications from the countries with emission targets. The effect appeared over many years during the period studied, particularly for solar energy technology. When we focus on countries with more stringent targets, the effect of the Kyoto Protocol is even stronger. For these countries, the Protocol's impact on the numbers of applications for international patent persisted strongly, even for wind energy technology. Moreover, we find a similar effect for the international patent applications filed in four developing countries that are large emitters of greenhouse gases: Brazil, China, India, and Mexico. These results suggest that the Kyoto Protocol stimulated international patenting activities from countries that are committed to stringent targets for climate mitigation. Our results endorse the importance of climate change agreements for international diffusion of technology.