With the issue of the still uncontrolled Indonesian airspace by foreign FIRs, especially above the Riau Islands and Natuna by the Singapore FIR based on agreements made by Indonesia and Singapore in 1995. There was a difference of opinion regarding the case of the FIR issue that had been happening all this time. Arrangements for the determination of FIR flight areas that refer to safety aspects often clash or are not in line with the sovereignty aspects of the borders of a country which can be a source of dispute between one country and another. This thesis aims to provide knowledge in the field of air law and to find out about the Indonesia-Singapore FIR Agreement in the Riau Islands and Natuna based on international law in particular the Chicago Convention 1944. The type of research that the author uses in the preparation of the thesis is to use normative legal research. Normative legal research is a research focuses on the positive law in the form of the International Conventions, The applicable International Agreement, The Customary Law and Legislation Rules associated with The Juridical Assessment Concerned.