The main purpose of this study is to identify the position of Islam religion and the position of Islamic law in the constitution of Malaysia, Brunei Darussalam and Indonesia that become a major issue in Muslim-majority countries. This is a qualitative and comparative study on the constitution of the three countries. The survey data include secondary data based on library research findings show that: (1) substantial approach is more appropriate that a formal approach in explaining the position of religion and state in the constitution of the Islamic countries. (2) In the Federal Constitution of Malaysia, the provisions of Islam as the official religion of the country do not imply that Islam is used as a national ideology and Malaysia do not have a legal system based on the Islamic Syariah. (3) In the Constitution of Brunei Darussalam, the provisions of Islam as the official religion do not imply that the basis of the Islamic state and Islamic law becomes the primary law in Brunei Darussalam. (4) In Indonesia, the Indonesian Constitution, UUD 1945, it is stated that the country is based on belief in one God but the word "religion" in the constitution is not only for Islam, but also other religions recognized by the state, such as: Protestant, Catholic, Hindu, and Buddha. The conclusion of this study is that not one country of the three countries researched (Malaysia, Brunei, and Indonesia) practice the concept Islamic state or the Islamic law despite the existence of provisions of Islam as the official religion in Malaysia and Brunei Darussalam and belief in one God in Indonesia.