This undergraduate thesis aims to explain the reason why Daerah Istimewa Yogyakarta decided to establish sister province relationship with Saint Petersburg Russia. As we know that, there is some cooperation of the sister province program by Daerah Istimewa Yogyakarta with some provinces, not only Saint Petersburg, and this is the reason why the writer wants to make a research in this interesting topic. To give the comprehensive understanding in this research, the writer will give an analysis about the reason behind the policy by government of Daerah Istimewa Yogyakarta to decide the cooperation in the program of sister province with Saint Petersburg, Russia. In this case, to answer the research question, the writer will use some theories and concept, as follows The Rational Actor Theory, International Cooperation Theory and The Concept of Sister City.