<p>Taiwan’s international space and its formal diplomatic engagement with Southeast Asia have been more limited because of China’s growing influence. To navigate this challenge, Southeast Asia has become one of the focuses of Taiwan’s New Southbound Policy. Through this policy, Taiwan has been trying to enhance its international role through its technological capability, knowledge, and innovation, especially via smart city development. This study examines how Taiwan utilizes smart city expertise as a form of science diplomacy to engage with Southeast Asian countries. A qualitative comparative case study of Thailand and Malaysia, supported by secondary sources, is applied in this study. The findings show that the two countries respond differently to Taiwan. These differences are shaped not only by technological capacity or urban development needs, but also by political constraints related to the One China Policy, partner country receptivity, and the involvement of non-state actors. Notably, the study shows that smart city expertise enables Taiwan to engage Southeast Asian countries by reinforcing its regional presence in science and technology without directly confronting China.</p>