An order of International Relations today has new actors, one of them is the city government or local government. Cooperation between the local government or city is framed in Sister City or Twin Cities cooperation. Bandung, is one of the cities in Indonesia that is very active and successful in Sister City cooperation. One of Bandung's Sister City cooperation is with Metropolitan City of Seoul since 2016. This research will focus on explaining the reason why Bandung City Government chose has Sister City Cooperation toward Seoul Metropolitan Government. In this study the authors use the qualitative method, direct interviews with the Staff of Government Cooperation Part of Bandung, and also using secondary data in the form of books, magazines, journals, internet, newspapers and other relevant sources. To analyze, the author uses the concept of sister city and the concept of paradiplomacy. The results of this study indicate that the Bandung City Government chose to cooperate with Seoul Metropolitan City Government because has interest to manage the urban planning seems like Seoul, cultural exchange and information about Smart City.