Abstract: The size of a nuclear reactor has increased from below 300 MWe to more than 1000 MWe to achieve better economies of scale since the 1950s. Across the 1970s and 1980s, severe nuclear accidents, completion time overrun, escalating construction cost, and strong negative public perception are among the main factors leading to a slowdown in nuclear energy developments. Post-Fukushima, nuclear energy remains an important option for addressing energy security and decarbonization for developing economies, especially those in the Association of South East Asian Nations (ASEAN). However, a Fukushima-scale accident occurring in ASEAN could lead to severe trans-boundary impacts to several ASEAN members due to close geographical proximity. With the emergence of small modular reactors (SMRs), the conceivable advantages of SMRs over large reactors in the ASEAN context is yet to be assessed. In response, this study provides an analysis on the economic, safety, and other aspects of SMRs, and a review on the developments in nuclear energy in ASEAN. Findings from this study suggest SMRs as a strategic option in ASEAN’s long-term energy planning. While SMRs are still under design and development (some under demonstration), ASEAN needs to build up competence in nuclear energy through training and education, and international and regional cooperation.