Urban air pollution is one of the top policy priorities in East Asia. It is well known that atmosphere is an integrated system that transcends national boundaries and therefore, cannot be protected without international cooperation. Studies have investigated the effectiveness of regional cooperation on air pollution mainly from a national perspective. Environmental cooperation, however, is not the sole responsibility of national authorities. Cities and sub-regions play an important role in strengthening the cooperation on regional air pollution. The report examines the potential for regional cooperation between local governments and suggests policy recommendations. We have identified the two pillars of successful environmental cooperation: 1) political leadership and 2) knowledge based on social learning. Political leadership is determined by stringent local efforts to reduce emissions. Strengthening domestic inter-city network of environmental cooperation is also crucial for international leadership. Leading by example together with appropriate financial contribution can set the agenda for cooperation and persuade other parties to collaborate. Cities and sub-regions are equipped with their own resources, such as research institutions and local governments for scientific research and international collaboration. These resources should be fully utilised to develop  knowledge based on social learning.