This article does describe concerning Islamic law existence in Indonesia legal system. The author writes that Islamic law that has became obeyed legal norms system by majority Muslim as living law. It has also been inherently dogma and belief of Islamic religion and in national policy towards legal development then becomes significant factors. Elaboration on Islamic law here focuses in historical approach and applies existence theory.The existence theory does figures Indonesia legal system at past, current and future times. This theory also proposed that Islamic law is exist in Indonesian law either in written and can find in various life's aspects and legal practices