The thesis discussed on the role and thoughts that were carried out by Ki Bagus Hadikusumo in formulating the basic state of Republic of Indonesia. The literature study was used as the method which contsisted of a series of activities namely searching, reading, recording, reviewing reports and library materials that contained relevant theories to the problems in revealing past events. The results showed that the basic state that was set on August 18, 1945 was not only a contribution from the nationalist group such as Muhammad Yamin, Mr. Soepomo, and Ir. Soekarno, however, there was a very big role that was played by the important Muhammadiyah figure, Ki Bagus Hadikusumo. Ki Bagus Hadikusumo also voiced his thoughts about the basic state in front of BPUPKI (Committee for Preparatory Work for Indonesian Independence) members for the first period. The proposals of the basic state that were conveyed by Ki Bagus Hadikusumo consisted of five contents. Each content contained the meaning that the teachings of Islam deserve to be used as a foundation in the state because Islam is a religion that teaches unity on the basis of solid brotherhood, prioritizes the economy and regulates national defense, helps to build a fair government and upholds justice. It also does not contradict even it is appropriate with our nationality, and shapes the physical and spiritual national as well as puts the high spirit of independence. In the second session, the result of the formulation of the basic state by the Panitia Sembilan (nine committees) that was commonly known as Piagam Jakarta (the Jakarta Charter) was presented. On August 18, 1945, before PPKI (The Preparatory Committee for Indonesian Independence) session, Ki Bagus Hadikusumo became a figure who had contributed greatly in maintaining the integrity of the nation, especially in the First Sila in Piagam Jakarta changed to be “Ketuhanan Yang Maha Esa” (God Almighty), as well as it was passed by PPKI members on August 18, 1945.