This paper provides the most comprehensive review to date of the interpretations ( decisions ) by the Council of Grand Justices on the Separation - of Powers Doctrine under the constitution of the Republic of China on Taiwan, which adopts a unique separation of powers among five branches. Section I explains the motives of writing, the goals to be achieved, and the methods used. Section I] investigates the theoretical underpinnings of the Doctrine to form a basis for the critical review of the interpretations. Section Ill analyzes the statistics about the interpretations on the Doctrine to see the tendency of development and the impact of the enactment of the 1 958 Statute Governing the Council of Grand Justices on the practice of constitutional adjudications. Section IV reviews the fifty- six interpretations on the Doctrine case by case under five categories, i.e., horizontal separation of powers, vertical separation of powers, checks and balances among branches, mutual respects among branches, and efforts in mointaining of constitutional democracy. Section V summarizes the findings and suggestions. The appendix includes four tables and four figures.