Tumen River forms part of the border between North Korea and Northeast China as well as between North Korea and Far East Russia. Tumen river area as a transborder subregion has been politically sensitive in the modern history laden with territorial claims and political disputes. During the Cold War period, the subregion became the routes for the camaraderie trade among three socialist countries, but the political, economic and cultural importance of the subregion had been marginal. However, the subregion began to be transformed under the effect of economic globalization after the end of the Cold War. The Greater Tumen Initiative (GTI), originally the Tumen River Area Development Programme (TRADP), is an intergovernmental cooperation mechanism since 1995, supported by the United Nations Development Programme (UNDP). Although GTI has not produced significant outcomes in terms of economic cooperation due to the disparities of political system and economic development among member countries, the subregion has already been transformed into a contact zone. More recently China is the most active at the GTI, which links it to the “Changjitu (Changchun–Jilin–Tumen) Development Plan,” which is expected to boost the economic development of three Northeast Provinces in Chinese territory. The spatial transformation of 'open border cities' and the cross-bordering mobility of those living there are examined, based on the field works and in-depth interviews. A special focus is put on Hunchun, one of the border cities in China, and Korean-Chinese (Chaoxianzu/Josenjok), who are arguably the most border-crossing since the border(s) became porous. Rather than reducing all the changes to the government policy, the cultural contestation in everyday life of Korean-Chinese in the changing urban space is highlighted. Moreover, the everyday practices and tactics by Korean-Chinese are investigated through the concepts of neighboring and social capital. The research has several implications. First, the border is no more the obstacle to the physical mobility than the integral forces in the lives of people residing in the subregion. Second, the Korean-Chinese are entitled to be the intermediaries in the subregion and beyond. Third, area studies, diaspora studies and the border studies needs to connected for the deeper understanding of the regionalization in the Northeast Asia.